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 $97.30   13.358%   $110.2973   $110.30   $110.30   $110.30  
  Purchase #2 $123.35   6.342%   $131.1729   $131.17   $131.15   $131.20  
  Purchase #3 $161.55   7.298%   $173.3399   $173.34   $173.35   $173.30  
  Purchase #4 $56.38   6.380%   $59.977   $59.98   $60.00   $60.00  
  Purchase #5 $209.91   7.652%   $225.9723   $225.97   $225.95   $226.00  
  Purchase #6 $138.68   6.188%   $147.2615   $147.26   $147.25   $147.30  
  Purchase #7 $168.52   13.772%   $191.7286   $191.73   $191.75   $191.70  
  7 purchase totals = $955.69       $1,039.7495   $1,039.75   $1,039.75   $1,039.80