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 $52.62   11.647%   $58.7487   $58.75   $58.75   $58.70  
  Purchase #2 $175.92   10.769%   $194.8648   $194.86   $194.85   $194.90  
  Purchase #3 $48.91   12.334%   $54.9426   $54.94   $54.95   $54.90  
  Purchase #4 $146.55   10.421%   $161.822   $161.82   $161.80   $161.80  
  Purchase #5 $248.99   3.684%   $258.1628   $258.16   $258.15   $258.20  
  Purchase #6 $108.60   9.160%   $118.5478   $118.55   $118.55   $118.50  
  Purchase #7 $216.46   6.133%   $229.7355   $229.74   $229.75   $229.70  
  7 purchase totals = $998.05       $1,076.8242   $1,076.82   $1,076.80   $1,076.70