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 $69.49   7.716%   $74.8518   $74.85   $74.85   $74.90  
  Purchase #2 $236.27   13.519%   $268.2113   $268.21   $268.20   $268.20  
  Purchase #3 $125.39   5.829%   $132.699   $132.70   $132.70   $132.70  
  Purchase #4 $174.89   12.769%   $197.2217   $197.22   $197.20   $197.20  
  Purchase #5 $10.90   7.301%   $11.6958   $11.70   $11.70   $11.70  
  Purchase #6 $53.89   13.454%   $61.1404   $61.14   $61.15   $61.10  
  Purchase #7 $132.93   13.812%   $151.2903   $151.29   $151.30   $151.30  
  7 purchase totals = $803.76       $897.1103   $897.11   $897.10   $897.10