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 $55.61   10.672%   $61.5447   $61.54   $61.55   $61.50  
  Purchase #2 $144.93   12.861%   $163.5694   $163.57   $163.55   $163.60  
  Purchase #3 $217.99   12.812%   $245.9189   $245.92   $245.90   $245.90  
  Purchase #4 $203.98   11.290%   $227.0093   $227.01   $227.00   $227.00  
  Purchase #5 $117.36   12.103%   $131.5641   $131.56   $131.55   $131.60  
  Purchase #6 $196.60   9.220%   $214.7265   $214.73   $214.75   $214.70  
  Purchase #7 $58.54   8.525%   $63.5305   $63.53   $63.55   $63.50  
  7 purchase totals = $995.01       $1,107.8634   $1,107.86   $1,107.85   $1,107.80