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 $168.43   8.379%   $182.5427   $182.54   $182.55   $182.50  
  Purchase #2 $94.73   7.684%   $102.0091   $102.01   $102.00   $102.00  
  Purchase #3 $24.55   7.275%   $26.336   $26.34   $26.35   $26.30  
  Purchase #4 $237.66   12.674%   $267.781   $267.78   $267.80   $267.80  
  Purchase #5 $142.78   13.517%   $162.0796   $162.08   $162.10   $162.10  
  Purchase #6 $66.51   13.384%   $75.4117   $75.41   $75.40   $75.40  
  Purchase #7 $239.75   3.300%   $247.6618   $247.66   $247.65   $247.70  
  7 purchase totals = $974.41       $1,063.8219   $1,063.82   $1,063.85   $1,063.80