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 $177.49   13.717%   $201.8363   $201.84   $201.85   $201.80  
  Purchase #2 $51.43   6.204%   $54.6207   $54.62   $54.60   $54.60  
  Purchase #3 $179.67   11.267%   $199.9134   $199.91   $199.90   $199.90  
  Purchase #4 $202.68   8.376%   $219.6565   $219.66   $219.65   $219.70  
  Purchase #5 $170.64   13.292%   $193.3215   $193.32   $193.30   $193.30  
  Purchase #6 $128.31   6.198%   $136.2627   $136.26   $136.25   $136.30  
  Purchase #7 $164.66   11.680%   $183.8923   $183.89   $183.90   $183.90  
  7 purchase totals = $1,074.88       $1,189.5034   $1,189.50   $1,189.45   $1,189.50