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 $198.92   4.186%   $207.2468   $207.25   $207.25   $207.20  
  Purchase #2 $91.91   11.718%   $102.68   $102.68   $102.70   $102.70  
  Purchase #3 $41.45   12.356%   $46.5716   $46.57   $46.55   $46.60  
  Purchase #4 $227.57   8.455%   $246.811   $246.81   $246.80   $246.80  
  Purchase #5 $154.47   11.374%   $172.0394   $172.04   $172.05   $172.00  
  Purchase #6 $116.70   13.750%   $132.7463   $132.75   $132.75   $132.70  
  Purchase #7 $91.81   6.634%   $97.9007   $97.90   $97.90   $97.90  
  7 purchase totals = $922.83       $1,005.9958   $1,006.00   $1,006.00   $1,005.90