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 $196.67   9.185%   $214.7341   $214.73   $214.75   $214.70  
  Purchase #2 $229.50   10.638%   $253.9142   $253.91   $253.90   $253.90  
  Purchase #3 $146.42   7.628%   $157.5889   $157.59   $157.60   $157.60  
  Purchase #4 $88.86   3.589%   $92.0492   $92.05   $92.05   $92.00  
  Purchase #5 $95.64   12.779%   $107.8618   $107.86   $107.85   $107.90  
  Purchase #6 $110.49   8.169%   $119.5159   $119.52   $119.50   $119.50  
  Purchase #7 $70.91   4.590%   $74.1648   $74.16   $74.15   $74.20  
  7 purchase totals = $938.49       $1,019.8289   $1,019.82   $1,019.80   $1,019.80