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 $67.70   11.714%   $75.6304   $75.63   $75.65   $75.60  
  Purchase #2 $160.57   12.502%   $180.6445   $180.64   $180.65   $180.60  
  Purchase #3 $97.62   6.370%   $103.8384   $103.84   $103.85   $103.80  
  Purchase #4 $244.55   11.418%   $272.4727   $272.47   $272.45   $272.50  
  Purchase #5 $64.67   3.473%   $66.916   $66.92   $66.90   $66.90  
  Purchase #6 $61.30   6.317%   $65.1723   $65.17   $65.15   $65.20  
  Purchase #7 $204.51   7.653%   $220.1612   $220.16   $220.15   $220.20  
  7 purchase totals = $900.92       $984.8355   $984.83   $984.80   $984.80