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 $228.75   6.418%   $243.4312   $243.43   $243.45   $243.40  
  Purchase #2 $59.63   11.626%   $66.5626   $66.56   $66.55   $66.60  
  Purchase #3 $218.32   3.569%   $226.1118   $226.11   $226.10   $226.10  
  Purchase #4 $98.27   13.175%   $111.2171   $111.22   $111.20   $111.20  
  Purchase #5 $205.88   4.295%   $214.7225   $214.72   $214.70   $214.70  
  Purchase #6 $58.90   9.352%   $64.4083   $64.41   $64.40   $64.40  
  Purchase #7 $156.46   13.398%   $177.4225   $177.42   $177.40   $177.40  
  7 purchase totals = $1,026.21       $1,103.8760   $1,103.87   $1,103.80   $1,103.80