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 $231.82   5.332%   $244.1806   $244.18   $244.20   $244.20  
  Purchase #2 $209.71   4.194%   $218.5052   $218.51   $218.50   $218.50  
  Purchase #3 $153.73   6.547%   $163.7947   $163.79   $163.80   $163.80  
  Purchase #4 $77.83   13.309%   $88.1884   $88.19   $88.20   $88.20  
  Purchase #5 $202.76   13.374%   $229.8771   $229.88   $229.90   $229.90  
  Purchase #6 $50.44   8.618%   $54.7869   $54.79   $54.80   $54.80  
  Purchase #7 $40.52   12.339%   $45.5198   $45.52   $45.50   $45.50  
  7 purchase totals = $966.81       $1,044.8527   $1,044.86   $1,044.90   $1,044.90