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 $209.49   10.633%   $231.7651   $231.77   $231.75   $231.80  
  Purchase #2 $5.69   4.657%   $5.955   $5.96   $5.95   $6.00  
  Purchase #3 $232.45   11.747%   $259.7559   $259.76   $259.75   $259.80  
  Purchase #4 $113.53   7.648%   $122.2128   $122.21   $122.20   $122.20  
  Purchase #5 $97.82   4.778%   $102.4938   $102.49   $102.50   $102.50  
  Purchase #6 $187.30   8.855%   $203.8854   $203.89   $203.90   $203.90  
  Purchase #7 $114.51   10.365%   $126.379   $126.38   $126.40   $126.40  
  7 purchase totals = $960.79       $1,052.4470   $1,052.46   $1,052.45   $1,052.60