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 $154.58   4.701%   $161.8468   $161.85   $161.85   $161.80  
  Purchase #2 $241.56   4.290%   $251.9229   $251.92   $251.90   $251.90  
  Purchase #3 $192.52   7.391%   $206.7492   $206.75   $206.75   $206.70  
  Purchase #4 $22.27   10.502%   $24.6088   $24.61   $24.60   $24.60  
  Purchase #5 $114.69   3.649%   $118.875   $118.88   $118.90   $118.90  
  Purchase #6 $148.56   7.474%   $159.6634   $159.66   $159.65   $159.70  
  Purchase #7 $249.38   11.324%   $277.6198   $277.62   $277.60   $277.60  
  7 purchase totals = $1,123.56       $1,201.2859   $1,201.29   $1,201.25   $1,201.20