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 $217.93   6.269%   $231.592   $231.59   $231.60   $231.60  
  Purchase #2 $163.84   10.205%   $180.5599   $180.56   $180.55   $180.60  
  Purchase #3 $71.49   13.215%   $80.9374   $80.94   $80.95   $80.90  
  Purchase #4 $164.29   4.172%   $171.1442   $171.14   $171.15   $171.10  
  Purchase #5 $153.87   3.432%   $159.1508   $159.15   $159.15   $159.20  
  Purchase #6 $141.88   12.271%   $159.2901   $159.29   $159.30   $159.30  
  Purchase #7 $197.79   7.142%   $211.9162   $211.92   $211.90   $211.90  
  7 purchase totals = $1,111.09       $1,194.5906   $1,194.59   $1,194.60   $1,194.60