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 $87.27   7.597%   $93.8999   $93.90   $93.90   $93.90  
  Purchase #2 $57.74   8.525%   $62.6623   $62.66   $62.65   $62.70  
  Purchase #3 $126.62   10.787%   $140.2785   $140.28   $140.30   $140.30  
  Purchase #4 $117.87   13.121%   $133.3357   $133.34   $133.35   $133.30  
  Purchase #5 $112.82   10.453%   $124.6131   $124.61   $124.60   $124.60  
  Purchase #6 $231.40   6.174%   $245.6866   $245.69   $245.70   $245.70  
  Purchase #7 $120.92   4.602%   $126.4847   $126.48   $126.50   $126.50  
  7 purchase totals = $854.64       $926.9608   $926.96   $927.00   $927.00