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 $244.92   7.172%   $262.4857   $262.49   $262.50   $262.50  
  Purchase #2 $37.94   4.408%   $39.6124   $39.61   $39.60   $39.60  
  Purchase #3 $159.52   3.697%   $165.4175   $165.42   $165.40   $165.40  
  Purchase #4 $7.99   11.654%   $8.9212   $8.92   $8.90   $8.90  
  Purchase #5 $201.34   4.331%   $210.06   $210.06   $210.05   $210.10  
  Purchase #6 $70.52   10.423%   $77.8703   $77.87   $77.85   $77.90  
  Purchase #7 $179.84   11.614%   $200.7266   $200.73   $200.75   $200.70  
  7 purchase totals = $902.07       $965.0937   $965.10   $965.05   $965.10