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 $181.65   8.269%   $196.6706   $196.67   $196.65   $196.70  
  Purchase #2 $98.63   4.370%   $102.9401   $102.94   $102.95   $102.90  
  Purchase #3 $170.25   10.179%   $187.5797   $187.58   $187.60   $187.60  
  Purchase #4 $226.56   10.113%   $249.472   $249.47   $249.45   $249.50  
  Purchase #5 $232.76   10.772%   $257.8329   $257.83   $257.85   $257.80  
  Purchase #6 $110.38   5.474%   $116.4222   $116.42   $116.40   $116.40  
  Purchase #7 $90.43   3.586%   $93.6728   $93.67   $93.65   $93.70  
  7 purchase totals = $1,110.66       $1,204.5903   $1,204.58   $1,204.55   $1,204.60