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 $114.74   6.153%   $121.8   $121.80   $121.80   $121.80  
  Purchase #2 $201.27   4.189%   $209.7012   $209.70   $209.70   $209.70  
  Purchase #3 $47.68   7.657%   $51.3309   $51.33   $51.35   $51.30  
  Purchase #4 $246.44   11.574%   $274.963   $274.96   $274.95   $275.00  
  Purchase #5 $38.42   5.780%   $40.6407   $40.64   $40.65   $40.60  
  Purchase #6 $88.66   9.304%   $96.9089   $96.91   $96.90   $96.90  
  Purchase #7 $16.85   7.650%   $18.139   $18.14   $18.15   $18.10  
  7 purchase totals = $754.06       $813.4837   $813.48   $813.50   $813.40