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 $72.55   3.407%   $75.0218   $75.02   $75.00   $75.00  
  Purchase #2 $247.82   11.797%   $277.0553   $277.06   $277.05   $277.10  
  Purchase #3 $233.28   4.666%   $244.1648   $244.16   $244.15   $244.20  
  Purchase #4 $240.62   5.426%   $253.676   $253.68   $253.70   $253.70  
  Purchase #5 $50.92   7.827%   $54.9055   $54.91   $54.90   $54.90  
  Purchase #6 $43.37   3.780%   $45.0094   $45.01   $45.00   $45.00  
  Purchase #7 $39.96   11.507%   $44.5582   $44.56   $44.55   $44.60  
  7 purchase totals = $928.52       $994.3910   $994.40   $994.35   $994.50