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 $96.73   8.214%   $104.6754   $104.68   $104.70   $104.70  
  Purchase #2 $203.29   13.637%   $231.0127   $231.01   $231.00   $231.00  
  Purchase #3 $206.39   10.702%   $228.4779   $228.48   $228.50   $228.50  
  Purchase #4 $57.28   5.154%   $60.2322   $60.23   $60.25   $60.20  
  Purchase #5 $229.98   13.717%   $261.5264   $261.53   $261.55   $261.50  
  Purchase #6 $58.38   7.845%   $62.9599   $62.96   $62.95   $63.00  
  Purchase #7 $101.61   7.761%   $109.496   $109.50   $109.50   $109.50  
  7 purchase totals = $953.66       $1,058.3805   $1,058.39   $1,058.45   $1,058.40