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 $88.84   4.761%   $93.0697   $93.07   $93.05   $93.10  
  Purchase #2 $213.90   12.613%   $240.8792   $240.88   $240.90   $240.90  
  Purchase #3 $12.82   13.318%   $14.5274   $14.53   $14.55   $14.50  
  Purchase #4 $215.30   12.842%   $242.9488   $242.95   $242.95   $242.90  
  Purchase #5 $48.83   13.301%   $55.3249   $55.32   $55.30   $55.30  
  Purchase #6 $96.69   5.131%   $101.6512   $101.65   $101.65   $101.70  
  Purchase #7 $181.82   7.160%   $194.8383   $194.84   $194.85   $194.80  
  7 purchase totals = $858.20       $943.2395   $943.24   $943.25   $943.20