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 $94.51   5.404%   $99.6173   $99.62   $99.60   $99.60  
  Purchase #2 $234.64   13.567%   $266.4736   $266.47   $266.45   $266.50  
  Purchase #3 $229.87   10.353%   $253.6684   $253.67   $253.65   $253.70  
  Purchase #4 $207.64   11.695%   $231.9235   $231.92   $231.90   $231.90  
  Purchase #5 $106.57   5.494%   $112.425   $112.43   $112.45   $112.40  
  Purchase #6 $115.84   3.849%   $120.2987   $120.30   $120.30   $120.30  
  Purchase #7 $51.98   5.195%   $54.6804   $54.68   $54.70   $54.70  
  7 purchase totals = $1,041.05       $1,139.0869   $1,139.09   $1,139.05   $1,139.10