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 $25.35   7.229%   $27.1826   $27.18   $27.20   $27.20  
  Purchase #2 $71.76   5.832%   $75.945   $75.95   $75.95   $75.90  
  Purchase #3 $97.62   13.227%   $110.5322   $110.53   $110.55   $110.50  
  Purchase #4 $174.94   11.853%   $195.6756   $195.68   $195.70   $195.70  
  Purchase #5 $181.98   11.687%   $203.248   $203.25   $203.25   $203.20  
  Purchase #6 $188.62   5.339%   $198.6904   $198.69   $198.70   $198.70  
  Purchase #7 $224.51   11.481%   $250.286   $250.29   $250.30   $250.30  
  7 purchase totals = $964.78       $1,061.5598   $1,061.57   $1,061.65   $1,061.50