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 $127.93   10.493%   $141.3537   $141.35   $141.35   $141.40  
  Purchase #2 $94.96   7.227%   $101.8228   $101.82   $101.80   $101.80  
  Purchase #3 $77.66   10.343%   $85.6924   $85.69   $85.70   $85.70  
  Purchase #4 $115.39   4.276%   $120.3241   $120.32   $120.30   $120.30  
  Purchase #5 $93.87   8.306%   $101.6668   $101.67   $101.65   $101.70  
  Purchase #6 $64.80   5.225%   $68.1858   $68.19   $68.20   $68.20  
  Purchase #7 $153.78   8.268%   $166.4945   $166.49   $166.50   $166.50  
  7 purchase totals = $728.39       $785.5401   $785.53   $785.50   $785.60