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 $67.73   8.544%   $73.5169   $73.52   $73.50   $73.50  
  Purchase #2 $238.69   4.365%   $249.1088   $249.11   $249.10   $249.10  
  Purchase #3 $6.70   13.587%   $7.6103   $7.61   $7.60   $7.60  
  Purchase #4 $210.37   13.714%   $239.2201   $239.22   $239.20   $239.20  
  Purchase #5 $237.57   9.144%   $259.2934   $259.29   $259.30   $259.30  
  Purchase #6 $55.39   6.166%   $58.8053   $58.81   $58.80   $58.80  
  Purchase #7 $221.72   11.513%   $247.2466   $247.25   $247.25   $247.20  
  7 purchase totals = $1,038.17       $1,134.8014   $1,134.81   $1,134.75   $1,134.70