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 $141.82   8.252%   $153.523   $153.52   $153.50   $153.50  
  Purchase #2 $80.94   9.865%   $88.9247   $88.92   $88.90   $88.90  
  Purchase #3 $56.83   5.126%   $59.7431   $59.74   $59.75   $59.70  
  Purchase #4 $245.48   7.116%   $262.9484   $262.95   $262.95   $262.90  
  Purchase #5 $22.91   9.745%   $25.1426   $25.14   $25.15   $25.10  
  Purchase #6 $48.40   12.499%   $54.4495   $54.45   $54.45   $54.40  
  Purchase #7 $236.67   13.458%   $268.521   $268.52   $268.50   $268.50  
  7 purchase totals = $833.05       $913.2523   $913.24   $913.20   $913.00