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 $119.82   6.549%   $127.667   $127.67   $127.65   $127.70  
  Purchase #2 $197.67   8.538%   $214.5471   $214.55   $214.55   $214.50  
  Purchase #3 $41.26   11.440%   $45.9801   $45.98   $46.00   $46.00  
  Purchase #4 $50.57   8.525%   $54.8811   $54.88   $54.90   $54.90  
  Purchase #5 $102.40   8.642%   $111.2494   $111.25   $111.25   $111.20  
  Purchase #6 $204.97   12.682%   $230.9643   $230.96   $230.95   $231.00  
  Purchase #7 $17.40   4.577%   $18.1964   $18.20   $18.20   $18.20  
  7 purchase totals = $734.09       $803.4854   $803.49   $803.50   $803.50