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 $111.93   13.512%   $127.054   $127.05   $127.05   $127.10  
  Purchase #2 $84.49   10.844%   $93.6521   $93.65   $93.65   $93.70  
  Purchase #3 $159.77   9.420%   $174.8203   $174.82   $174.80   $174.80  
  Purchase #4 $166.72   8.690%   $181.208   $181.21   $181.20   $181.20  
  Purchase #5 $51.76   7.592%   $55.6896   $55.69   $55.70   $55.70  
  Purchase #6 $152.28   13.502%   $172.8408   $172.84   $172.85   $172.80  
  Purchase #7 $97.64   3.467%   $101.0252   $101.03   $101.05   $101.00  
  7 purchase totals = $824.59       $906.2900   $906.29   $906.30   $906.30