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 $60.33   10.330%   $66.5621   $66.56   $66.55   $66.60  
  Purchase #2 $95.73   11.708%   $106.9381   $106.94   $106.95   $106.90  
  Purchase #3 $250.31   11.398%   $278.8403   $278.84   $278.85   $278.80  
  Purchase #4 $53.92   10.840%   $59.7649   $59.76   $59.75   $59.80  
  Purchase #5 $218.50   9.670%   $239.629   $239.63   $239.65   $239.60  
  Purchase #6 $187.30   3.645%   $194.1271   $194.13   $194.15   $194.10  
  Purchase #7 $188.87   8.395%   $204.7256   $204.73   $204.75   $204.70  
  7 purchase totals = $1,054.96       $1,150.5871   $1,150.59   $1,150.65   $1,150.50