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 $89.78   3.637%   $93.0453   $93.05   $93.05   $93.00  
  Purchase #2 $210.61   7.346%   $226.0814   $226.08   $226.10   $226.10  
  Purchase #3 $9.83   13.733%   $11.18   $11.18   $11.20   $11.20  
  Purchase #4 $186.39   7.425%   $200.2295   $200.23   $200.25   $200.20  
  Purchase #5 $232.72   13.417%   $263.944   $263.94   $263.95   $263.90  
  Purchase #6 $59.28   5.774%   $62.7028   $62.70   $62.70   $62.70  
  Purchase #7 $38.45   4.794%   $40.2933   $40.29   $40.30   $40.30  
  7 purchase totals = $827.06       $897.4763   $897.47   $897.55   $897.40