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 $88.58   6.649%   $94.4697   $94.47   $94.45   $94.50  
  Purchase #2 $85.75   7.674%   $92.3305   $92.33   $92.35   $92.30  
  Purchase #3 $226.71   7.282%   $243.219   $243.22   $243.20   $243.20  
  Purchase #4 $78.56   3.488%   $81.3002   $81.30   $81.30   $81.30  
  Purchase #5 $91.64   6.459%   $97.559   $97.56   $97.55   $97.60  
  Purchase #6 $232.88   5.805%   $246.3987   $246.40   $246.40   $246.40  
  Purchase #7 $26.64   8.152%   $28.8117   $28.81   $28.80   $28.80  
  7 purchase totals = $830.76       $884.0888   $884.09   $884.05   $884.10