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 $211.89   12.799%   $239.0098   $239.01   $239.00   $239.00  
  Purchase #2 $90.54   13.176%   $102.4696   $102.47   $102.45   $102.50  
  Purchase #3 $52.54   7.722%   $56.5971   $56.60   $56.60   $56.60  
  Purchase #4 $160.25   5.807%   $169.5557   $169.56   $169.55   $169.60  
  Purchase #5 $87.53   8.742%   $95.1819   $95.18   $95.20   $95.20  
  Purchase #6 $143.48   12.767%   $161.7981   $161.80   $161.80   $161.80  
  Purchase #7 $155.64   9.561%   $170.5207   $170.52   $170.50   $170.50  
  7 purchase totals = $901.87       $995.1329   $995.14   $995.10   $995.20