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 $30.38   4.510%   $31.7501   $31.75   $31.75   $31.80  
  Purchase #2 $79.85   8.750%   $86.8369   $86.84   $86.85   $86.80  
  Purchase #3 $83.46   11.190%   $92.7992   $92.80   $92.80   $92.80  
  Purchase #4 $172.50   3.870%   $179.1758   $179.18   $179.20   $179.20  
  Purchase #5 $34.65   9.334%   $37.8842   $37.88   $37.90   $37.90  
  Purchase #6 $89.78   4.353%   $93.6881   $93.69   $93.70   $93.70  
  Purchase #7 $216.66   9.544%   $237.338   $237.34   $237.35   $237.30  
  7 purchase totals = $707.28       $759.4723   $759.48   $759.55   $759.50