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 $201.45   6.108%   $213.7546   $213.75   $213.75   $213.80  
  Purchase #2 $242.93   9.586%   $266.2173   $266.22   $266.20   $266.20  
  Purchase #3 $99.58   11.206%   $110.7389   $110.74   $110.75   $110.70  
  Purchase #4 $214.84   6.766%   $229.3761   $229.38   $229.40   $229.40  
  Purchase #5 $125.77   7.354%   $135.0191   $135.02   $135.00   $135.00  
  Purchase #6 $116.75   4.354%   $121.8333   $121.83   $121.85   $121.80  
  Purchase #7 $174.60   6.582%   $186.0922   $186.09   $186.10   $186.10  
  7 purchase totals = $1,175.92       $1,263.0315   $1,263.03   $1,263.05   $1,263.00