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 $204.62   11.242%   $227.6234   $227.62   $227.60   $227.60  
  Purchase #2 $239.83   7.565%   $257.9731   $257.97   $257.95   $258.00  
  Purchase #3 $209.44   5.826%   $221.642   $221.64   $221.65   $221.60  
  Purchase #4 $59.28   4.288%   $61.8219   $61.82   $61.80   $61.80  
  Purchase #5 $53.56   12.256%   $60.1243   $60.12   $60.10   $60.10  
  Purchase #6 $169.39   8.399%   $183.6171   $183.62   $183.60   $183.60  
  Purchase #7 $110.77   10.547%   $122.4529   $122.45   $122.45   $122.50  
  7 purchase totals = $1,046.89       $1,135.2547   $1,135.24   $1,135.15   $1,135.20