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 $214.98   12.241%   $241.2957   $241.30   $241.30   $241.30  
  Purchase #2 $31.58   4.242%   $32.9196   $32.92   $32.90   $32.90  
  Purchase #3 $47.34   7.834%   $51.0486   $51.05   $51.05   $51.00  
  Purchase #4 $99.73   4.587%   $104.3046   $104.30   $104.30   $104.30  
  Purchase #5 $142.26   5.153%   $149.5907   $149.59   $149.60   $149.60  
  Purchase #6 $241.65   6.350%   $256.9948   $256.99   $257.00   $257.00  
  Purchase #7 $83.43   8.266%   $90.3263   $90.33   $90.35   $90.30  
  7 purchase totals = $860.97       $926.4803   $926.48   $926.50   $926.40