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 $60.53   11.403%   $67.4322   $67.43   $67.45   $67.40  
  Purchase #2 $92.73   5.419%   $97.755   $97.76   $97.75   $97.80  
  Purchase #3 $149.29   13.372%   $169.2531   $169.25   $169.25   $169.30  
  Purchase #4 $167.64   7.334%   $179.9347   $179.93   $179.95   $179.90  
  Purchase #5 $48.28   11.201%   $53.6878   $53.69   $53.70   $53.70  
  Purchase #6 $60.81   11.282%   $67.6706   $67.67   $67.65   $67.70  
  Purchase #7 $228.97   12.413%   $257.392   $257.39   $257.40   $257.40  
  7 purchase totals = $808.25       $893.1254   $893.12   $893.15   $893.20