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 $92.78   5.817%   $98.177   $98.18   $98.20   $98.20  
  Purchase #2 $129.27   6.735%   $137.9763   $137.98   $138.00   $138.00  
  Purchase #3 $110.98   13.862%   $126.364   $126.36   $126.35   $126.40  
  Purchase #4 $247.33   10.430%   $273.1265   $273.13   $273.15   $273.10  
  Purchase #5 $186.66   11.834%   $208.7493   $208.75   $208.75   $208.70  
  Purchase #6 $23.52   8.276%   $25.4665   $25.47   $25.45   $25.50  
  Purchase #7 $141.48   10.528%   $156.375   $156.38   $156.40   $156.40  
  7 purchase totals = $932.02       $1,026.2346   $1,026.25   $1,026.30   $1,026.30