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 $213.51   8.749%   $232.19   $232.19   $232.20   $232.20  
  Purchase #2 $211.67   7.138%   $226.779   $226.78   $226.80   $226.80  
  Purchase #3 $245.98   9.263%   $268.7651   $268.77   $268.75   $268.80  
  Purchase #4 $67.25   3.188%   $69.3939   $69.39   $69.40   $69.40  
  Purchase #5 $232.66   9.484%   $254.7255   $254.73   $254.75   $254.70  
  Purchase #6 $42.37   4.338%   $44.208   $44.21   $44.20   $44.20  
  Purchase #7 $235.52   5.436%   $248.3229   $248.32   $248.30   $248.30  
  7 purchase totals = $1,248.96       $1,344.3844   $1,344.39   $1,344.40   $1,344.40