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 $205.45   8.214%   $222.3257   $222.33   $222.35   $222.30  
  Purchase #2 $51.53   3.668%   $53.4201   $53.42   $53.40   $53.40  
  Purchase #3 $78.58   6.775%   $83.9038   $83.90   $83.90   $83.90  
  Purchase #4 $82.46   7.355%   $88.5249   $88.52   $88.50   $88.50  
  Purchase #5 $51.85   3.771%   $53.8053   $53.81   $53.80   $53.80  
  Purchase #6 $217.73   6.847%   $232.638   $232.64   $232.65   $232.60  
  Purchase #7 $207.33   9.475%   $226.9745   $226.97   $226.95   $227.00  
  7 purchase totals = $894.93       $961.5923   $961.59   $961.55   $961.50