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 $86.72   7.746%   $93.4373   $93.44   $93.45   $93.40  
  Purchase #2 $234.59   4.272%   $244.6117   $244.61   $244.60   $244.60  
  Purchase #3 $76.96   13.308%   $87.2018   $87.20   $87.20   $87.20  
  Purchase #4 $126.53   9.843%   $138.9843   $138.98   $139.00   $139.00  
  Purchase #5 $149.91   13.844%   $170.6635   $170.66   $170.65   $170.70  
  Purchase #6 $85.42   3.340%   $88.273   $88.27   $88.25   $88.30  
  Purchase #7 $129.69   10.147%   $142.8496   $142.85   $142.85   $142.80  
  7 purchase totals = $889.82       $966.0212   $966.01   $966.00   $966.00