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 $204.37   9.233%   $223.2395   $223.24   $223.25   $223.20  
  Purchase #2 $49.66   3.368%   $51.3325   $51.33   $51.35   $51.30  
  Purchase #3 $15.95   11.455%   $17.7771   $17.78   $17.80   $17.80  
  Purchase #4 $107.93   4.425%   $112.7059   $112.71   $112.70   $112.70  
  Purchase #5 $198.28   4.483%   $207.1689   $207.17   $207.15   $207.20  
  Purchase #6 $181.75   11.762%   $203.1274   $203.13   $203.15   $203.10  
  Purchase #7 $177.57   8.661%   $192.9493   $192.95   $192.95   $192.90  
  7 purchase totals = $935.51       $1,008.3006   $1,008.31   $1,008.35   $1,008.20