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 $168.65   9.271%   $184.2855   $184.29   $184.30   $184.30  
  Purchase #2 $104.75   3.444%   $108.3576   $108.36   $108.35   $108.40  
  Purchase #3 $19.86   13.809%   $22.6025   $22.60   $22.60   $22.60  
  Purchase #4 $48.41   13.547%   $54.9681   $54.97   $54.95   $55.00  
  Purchase #5 $146.31   4.164%   $152.4023   $152.40   $152.40   $152.40  
  Purchase #6 $10.86   13.470%   $12.3228   $12.32   $12.30   $12.30  
  Purchase #7 $204.33   8.522%   $221.743   $221.74   $221.75   $221.70  
  7 purchase totals = $703.17       $756.6818   $756.68   $756.65   $756.70