Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $179.53   13.229%   $203.28   $203.28   $203.30   $203.30  
  Purchase #2 $186.44   10.406%   $205.8409   $205.84   $205.85   $205.80  
  Purchase #3 $152.69   12.715%   $172.1045   $172.10   $172.10   $172.10  
  Purchase #4 $118.46   7.701%   $127.5826   $127.58   $127.60   $127.60  
  Purchase #5 $189.67   6.154%   $201.3423   $201.34   $201.35   $201.30  
  Purchase #6 $184.72   8.176%   $199.8227   $199.82   $199.80   $199.80  
  Purchase #7 $248.61   10.155%   $273.8563   $273.86   $273.85   $273.90  
  7 purchase totals = $1,260.12       $1,383.8293   $1,383.82   $1,383.85   $1,383.80