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 $188.98   13.202%   $213.9291   $213.93   $213.95   $213.90  
  Purchase #2 $144.94   4.321%   $151.2029   $151.20   $151.20   $151.20  
  Purchase #3 $63.67   5.502%   $67.1731   $67.17   $67.15   $67.20  
  Purchase #4 $141.43   9.301%   $154.5844   $154.58   $154.60   $154.60  
  Purchase #5 $181.80   6.525%   $193.6625   $193.66   $193.65   $193.70  
  Purchase #6 $39.53   3.177%   $40.7859   $40.79   $40.80   $40.80  
  Purchase #7 $197.81   13.672%   $224.8546   $224.85   $224.85   $224.90  
  7 purchase totals = $958.16       $1,046.1925   $1,046.18   $1,046.20   $1,046.30