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 $172.34   12.140%   $193.2621   $193.26   $193.25   $193.30  
  Purchase #2 $182.57   8.315%   $197.7507   $197.75   $197.75   $197.80  
  Purchase #3 $229.45   5.316%   $241.6476   $241.65   $241.65   $241.60  
  Purchase #4 $52.72   7.539%   $56.6946   $56.69   $56.70   $56.70  
  Purchase #5 $70.66   3.475%   $73.1154   $73.12   $73.10   $73.10  
  Purchase #6 $140.28   5.648%   $148.203   $148.20   $148.20   $148.20  
  Purchase #7 $94.72   6.494%   $100.8711   $100.87   $100.85   $100.90  
  7 purchase totals = $942.74       $1,011.5445   $1,011.54   $1,011.50   $1,011.60