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 $83.47   12.198%   $93.6517   $93.65   $93.65   $93.70  
  Purchase #2 $13.40   10.720%   $14.8365   $14.84   $14.85   $14.80  
  Purchase #3 $196.87   6.102%   $208.883   $208.88   $208.90   $208.90  
  Purchase #4 $239.82   4.521%   $250.6623   $250.66   $250.65   $250.70  
  Purchase #5 $157.93   12.595%   $177.8213   $177.82   $177.80   $177.80  
  Purchase #6 $210.64   12.355%   $236.6646   $236.66   $236.65   $236.70  
  Purchase #7 $11.88   4.804%   $12.4507   $12.45   $12.45   $12.50  
  7 purchase totals = $914.01       $994.9701   $994.96   $994.95   $995.10