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 $238.88   12.163%   $267.935   $267.94   $267.95   $267.90  
  Purchase #2 $68.79   11.355%   $76.6011   $76.60   $76.60   $76.60  
  Purchase #3 $188.56   9.647%   $206.7504   $206.75   $206.75   $206.80  
  Purchase #4 $122.84   8.800%   $133.6499   $133.65   $133.65   $133.60  
  Purchase #5 $231.95   6.810%   $247.7458   $247.75   $247.75   $247.70  
  Purchase #6 $113.57   5.173%   $119.445   $119.45   $119.45   $119.40  
  Purchase #7 $191.70   8.142%   $207.3082   $207.31   $207.30   $207.30  
  7 purchase totals = $1,156.29       $1,259.4354   $1,259.45   $1,259.45   $1,259.30