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 $183.92   10.568%   $203.3567   $203.36   $203.35   $203.40  
  Purchase #2 $125.60   5.236%   $132.1764   $132.18   $132.20   $132.20  
  Purchase #3 $159.46   10.112%   $175.5846   $175.58   $175.60   $175.60  
  Purchase #4 $192.53   13.183%   $217.9112   $217.91   $217.90   $217.90  
  Purchase #5 $147.56   13.561%   $167.5706   $167.57   $167.55   $167.60  
  Purchase #6 $120.32   12.176%   $134.9702   $134.97   $134.95   $135.00  
  Purchase #7 $21.54   9.260%   $23.5346   $23.53   $23.55   $23.50  
  7 purchase totals = $950.93       $1,055.1043   $1,055.10   $1,055.10   $1,055.20