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 $69.92   4.692%   $73.2006   $73.20   $73.20   $73.20  
  Purchase #2 $88.82   6.447%   $94.5462   $94.55   $94.55   $94.50  
  Purchase #3 $129.61   6.143%   $137.5719   $137.57   $137.55   $137.60  
  Purchase #4 $131.83   7.752%   $142.0495   $142.05   $142.05   $142.00  
  Purchase #5 $100.39   6.521%   $106.9364   $106.94   $106.95   $106.90  
  Purchase #6 $10.58   13.518%   $12.0102   $12.01   $12.00   $12.00  
  Purchase #7 $225.34   4.470%   $235.4127   $235.41   $235.40   $235.40  
  7 purchase totals = $756.49       $801.7275   $801.73   $801.70   $801.60