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 $243.51   5.578%   $257.093   $257.09   $257.10   $257.10  
  Purchase #2 $86.34   13.148%   $97.692   $97.69   $97.70   $97.70  
  Purchase #3 $62.67   6.317%   $66.6289   $66.63   $66.65   $66.60  
  Purchase #4 $190.66   3.656%   $197.6305   $197.63   $197.65   $197.60  
  Purchase #5 $122.41   3.628%   $126.851   $126.85   $126.85   $126.90  
  Purchase #6 $39.97   11.306%   $44.489   $44.49   $44.50   $44.50  
  Purchase #7 $228.58   7.359%   $245.4012   $245.40   $245.40   $245.40  
  7 purchase totals = $974.14       $1,035.7856   $1,035.78   $1,035.85   $1,035.80