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 $245.85   12.771%   $277.2475   $277.25   $277.25   $277.20  
  Purchase #2 $224.34   4.670%   $234.8167   $234.82   $234.80   $234.80  
  Purchase #3 $110.91   6.275%   $117.8696   $117.87   $117.85   $117.90  
  Purchase #4 $52.35   4.856%   $54.8921   $54.89   $54.90   $54.90  
  Purchase #5 $46.73   13.561%   $53.0671   $53.07   $53.05   $53.10  
  Purchase #6 $231.47   5.315%   $243.7726   $243.77   $243.75   $243.80  
  Purchase #7 $66.43   13.224%   $75.2147   $75.21   $75.20   $75.20  
  7 purchase totals = $978.08       $1,056.8803   $1,056.88   $1,056.80   $1,056.90