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 $188.47   6.673%   $201.0466   $201.05   $201.05   $201.00  
  Purchase #2 $225.64   6.165%   $239.5507   $239.55   $239.55   $239.60  
  Purchase #3 $12.35   8.206%   $13.3634   $13.36   $13.35   $13.40  
  Purchase #4 $184.56   9.666%   $202.3996   $202.40   $202.40   $202.40  
  Purchase #5 $42.45   6.792%   $45.3332   $45.33   $45.35   $45.30  
  Purchase #6 $101.68   9.210%   $111.0447   $111.04   $111.05   $111.00  
  Purchase #7 $171.85   3.276%   $177.4798   $177.48   $177.50   $177.50  
  7 purchase totals = $927.00       $990.2180   $990.21   $990.25   $990.20