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 $60.40   7.351%   $64.84   $64.84   $64.85   $64.80  
  Purchase #2 $119.79   13.461%   $135.9149   $135.91   $135.90   $135.90  
  Purchase #3 $158.76   5.507%   $167.5029   $167.50   $167.50   $167.50  
  Purchase #4 $244.51   13.517%   $277.5604   $277.56   $277.55   $277.60  
  Purchase #5 $187.56   11.667%   $209.4426   $209.44   $209.45   $209.40  
  Purchase #6 $170.39   9.567%   $186.6912   $186.69   $186.70   $186.70  
  Purchase #7 $22.45   12.429%   $25.2403   $25.24   $25.25   $25.20  
  7 purchase totals = $963.86       $1,067.1923   $1,067.18   $1,067.20   $1,067.10