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 $52.37   11.372%   $58.3255   $58.33   $58.35   $58.30  
  Purchase #2 $191.47   5.266%   $201.5528   $201.55   $201.55   $201.60  
  Purchase #3 $101.77   13.558%   $115.568   $115.57   $115.55   $115.60  
  Purchase #4 $206.44   3.327%   $213.3083   $213.31   $213.30   $213.30  
  Purchase #5 $67.60   12.865%   $76.2967   $76.30   $76.30   $76.30  
  Purchase #6 $121.44   12.305%   $136.3832   $136.38   $136.40   $136.40  
  Purchase #7 $112.46   8.163%   $121.6401   $121.64   $121.65   $121.60  
  7 purchase totals = $853.55       $923.0746   $923.08   $923.10   $923.10