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 $53.50   12.195%   $60.0243   $60.02   $60.00   $60.00  
  Purchase #2 $103.93   12.159%   $116.5668   $116.57   $116.55   $116.60  
  Purchase #3 $40.97   7.785%   $44.1595   $44.16   $44.15   $44.20  
  Purchase #4 $131.30   11.851%   $146.8604   $146.86   $146.85   $146.90  
  Purchase #5 $247.32   3.472%   $255.907   $255.91   $255.90   $255.90  
  Purchase #6 $38.99   13.485%   $44.2478   $44.25   $44.25   $44.20  
  Purchase #7 $81.45   11.753%   $91.0228   $91.02   $91.00   $91.00  
  7 purchase totals = $697.46       $758.7886   $758.79   $758.70   $758.80