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 $46.38   3.107%   $47.821   $47.82   $47.80   $47.80  
  Purchase #2 $81.27   3.219%   $83.8861   $83.89   $83.90   $83.90  
  Purchase #3 $16.78   11.672%   $18.7386   $18.74   $18.75   $18.70  
  Purchase #4 $71.97   11.798%   $80.461   $80.46   $80.45   $80.50  
  Purchase #5 $237.39   3.597%   $245.9289   $245.93   $245.95   $245.90  
  Purchase #6 $155.29   13.185%   $175.765   $175.77   $175.75   $175.80  
  Purchase #7 $62.96   11.241%   $70.0373   $70.04   $70.05   $70.00  
  7 purchase totals = $672.04       $722.6379   $722.65   $722.65   $722.60