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 $63.27   5.830%   $66.9586   $66.96   $66.95   $67.00  
  Purchase #2 $244.35   4.772%   $256.0104   $256.01   $256.00   $256.00  
  Purchase #3 $121.50   8.484%   $131.8081   $131.81   $131.80   $131.80  
  Purchase #4 $177.67   7.667%   $191.292   $191.29   $191.30   $191.30  
  Purchase #5 $35.64   3.839%   $37.0082   $37.01   $37.00   $37.00  
  Purchase #6 $118.59   12.140%   $132.9868   $132.99   $133.00   $133.00  
  Purchase #7 $233.35   3.191%   $240.7962   $240.80   $240.80   $240.80  
  7 purchase totals = $994.37       $1,056.8603   $1,056.87   $1,056.85   $1,056.90