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 $62.99   13.704%   $71.6221   $71.62   $71.60   $71.60  
  Purchase #2 $201.84   12.641%   $227.3546   $227.35   $227.35   $227.40  
  Purchase #3 $42.38   12.556%   $47.7012   $47.70   $47.70   $47.70  
  Purchase #4 $239.45   5.415%   $252.4162   $252.42   $252.40   $252.40  
  Purchase #5 $249.32   11.457%   $277.8846   $277.88   $277.90   $277.90  
  Purchase #6 $215.62   10.361%   $237.9604   $237.96   $237.95   $238.00  
  Purchase #7 $228.78   10.510%   $252.8248   $252.82   $252.80   $252.80  
  7 purchase totals = $1,240.38       $1,367.7639   $1,367.75   $1,367.70   $1,367.80