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 $124.63   11.594%   $139.0796   $139.08   $139.10   $139.10  
  Purchase #2 $232.89   10.395%   $257.0989   $257.10   $257.10   $257.10  
  Purchase #3 $153.77   10.193%   $169.4438   $169.44   $169.45   $169.40  
  Purchase #4 $87.67   10.369%   $96.7605   $96.76   $96.75   $96.80  
  Purchase #5 $48.44   5.195%   $50.9565   $50.96   $50.95   $51.00  
  Purchase #6 $165.53   8.375%   $179.3931   $179.39   $179.40   $179.40  
  Purchase #7 $170.29   3.304%   $175.9164   $175.92   $175.90   $175.90  
  7 purchase totals = $983.22       $1,068.6488   $1,068.65   $1,068.65   $1,068.70