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 $76.33   11.295%   $84.9515   $84.95   $84.95   $85.00  
  Purchase #2 $244.67   6.461%   $260.4781   $260.48   $260.50   $260.50  
  Purchase #3 $56.89   5.650%   $60.1043   $60.10   $60.10   $60.10  
  Purchase #4 $77.76   4.434%   $81.2079   $81.21   $81.20   $81.20  
  Purchase #5 $203.39   6.563%   $216.7385   $216.74   $216.75   $216.70  
  Purchase #6 $203.52   9.279%   $222.4046   $222.40   $222.40   $222.40  
  Purchase #7 $48.79   13.588%   $55.4196   $55.42   $55.40   $55.40  
  7 purchase totals = $911.35       $981.3045   $981.30   $981.30   $981.30