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 $83.71   5.390%   $88.222   $88.22   $88.20   $88.20  
  Purchase #2 $112.64   4.814%   $118.0625   $118.06   $118.05   $118.10  
  Purchase #3 $56.98   7.312%   $61.1464   $61.15   $61.15   $61.10  
  Purchase #4 $211.93   11.772%   $236.8784   $236.88   $236.90   $236.90  
  Purchase #5 $242.37   12.859%   $273.5364   $273.54   $273.55   $273.50  
  Purchase #6 $147.61   12.604%   $166.2148   $166.21   $166.20   $166.20  
  Purchase #7 $207.35   9.315%   $226.6647   $226.66   $226.65   $226.70  
  7 purchase totals = $1,062.59       $1,170.7252   $1,170.72   $1,170.70   $1,170.70