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 $81.34   11.819%   $90.9536   $90.95   $90.95   $91.00  
  Purchase #2 $88.73   9.131%   $96.8319   $96.83   $96.85   $96.80  
  Purchase #3 $154.80   4.657%   $162.009   $162.01   $162.00   $162.00  
  Purchase #4 $43.27   12.674%   $48.754   $48.75   $48.75   $48.80  
  Purchase #5 $205.42   8.246%   $222.3589   $222.36   $222.35   $222.40  
  Purchase #6 $235.68   10.705%   $260.9095   $260.91   $260.90   $260.90  
  Purchase #7 $67.86   7.295%   $72.8104   $72.81   $72.80   $72.80  
  7 purchase totals = $877.10       $954.6273   $954.62   $954.60   $954.70