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 $26.38   4.713%   $27.6233   $27.62   $27.60   $27.60  
  Purchase #2 $39.83   3.691%   $41.3001   $41.30   $41.30   $41.30  
  Purchase #3 $181.44   11.267%   $201.8828   $201.88   $201.90   $201.90  
  Purchase #4 $178.67   10.797%   $197.961   $197.96   $197.95   $198.00  
  Purchase #5 $46.79   5.329%   $49.2834   $49.28   $49.30   $49.30  
  Purchase #6 $147.86   3.226%   $152.63   $152.63   $152.65   $152.60  
  Purchase #7 $174.98   12.797%   $197.3722   $197.37   $197.35   $197.40  
  7 purchase totals = $795.95       $868.0528   $868.04   $868.05   $868.10