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 $75.82   6.852%   $81.0152   $81.02   $81.00   $81.00  
  Purchase #2 $183.98   5.227%   $193.5966   $193.60   $193.60   $193.60  
  Purchase #3 $203.95   11.197%   $226.7863   $226.79   $226.80   $226.80  
  Purchase #4 $42.37   12.403%   $47.6252   $47.63   $47.65   $47.60  
  Purchase #5 $53.39   6.273%   $56.7392   $56.74   $56.75   $56.70  
  Purchase #6 $95.93   4.494%   $100.2411   $100.24   $100.25   $100.20  
  Purchase #7 $216.91   6.605%   $231.2369   $231.24   $231.25   $231.20  
  7 purchase totals = $872.35       $937.2405   $937.26   $937.30   $937.10