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 $126.82   11.380%   $141.2521   $141.25   $141.25   $141.30  
  Purchase #2 $68.82   8.761%   $74.8493   $74.85   $74.85   $74.80  
  Purchase #3 $33.92   11.529%   $37.8306   $37.83   $37.85   $37.80  
  Purchase #4 $98.95   9.724%   $108.5719   $108.57   $108.55   $108.60  
  Purchase #5 $170.63   10.845%   $189.1348   $189.13   $189.15   $189.10  
  Purchase #6 $142.26   6.830%   $151.9764   $151.98   $152.00   $152.00  
  Purchase #7 $181.86   7.103%   $194.7775   $194.78   $194.80   $194.80  
  7 purchase totals = $823.26       $898.3926   $898.39   $898.45   $898.40