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 $43.49   9.464%   $47.6059   $47.61   $47.60   $47.60  
  Purchase #2 $76.91   5.571%   $81.1947   $81.19   $81.20   $81.20  
  Purchase #3 $189.33   8.245%   $204.9403   $204.94   $204.95   $204.90  
  Purchase #4 $245.49   7.176%   $263.1064   $263.11   $263.10   $263.10  
  Purchase #5 $186.98   10.193%   $206.0389   $206.04   $206.05   $206.00  
  Purchase #6 $10.73   6.740%   $11.4532   $11.45   $11.45   $11.50  
  Purchase #7 $70.97   13.615%   $80.6326   $80.63   $80.65   $80.60  
  7 purchase totals = $823.90       $894.9720   $894.97   $895.00   $894.90