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 $53.52   3.853%   $55.5821   $55.58   $55.60   $55.60  
  Purchase #2 $246.50   8.124%   $266.5257   $266.53   $266.55   $266.50  
  Purchase #3 $113.31   10.835%   $125.5871   $125.59   $125.60   $125.60  
  Purchase #4 $124.45   3.438%   $128.7286   $128.73   $128.75   $128.70  
  Purchase #5 $127.96   5.216%   $134.6344   $134.63   $134.65   $134.60  
  Purchase #6 $114.74   8.244%   $124.1992   $124.20   $124.20   $124.20  
  Purchase #7 $51.50   10.755%   $57.0388   $57.04   $57.05   $57.00  
  7 purchase totals = $831.98       $892.2959   $892.30   $892.40   $892.20