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 $210.92   10.464%   $232.9907   $232.99   $233.00   $233.00  
  Purchase #2 $18.47   11.657%   $20.623   $20.62   $20.60   $20.60  
  Purchase #3 $180.90   9.248%   $197.6296   $197.63   $197.65   $197.60  
  Purchase #4 $225.88   8.698%   $245.527   $245.53   $245.55   $245.50  
  Purchase #5 $191.99   9.331%   $209.9046   $209.90   $209.90   $209.90  
  Purchase #6 $104.48   13.373%   $118.4521   $118.45   $118.45   $118.50  
  Purchase #7 $51.63   4.463%   $53.9342   $53.93   $53.95   $53.90  
  7 purchase totals = $984.27       $1,079.0612   $1,079.05   $1,079.10   $1,079.00