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 $197.41   8.421%   $214.0339   $214.03   $214.05   $214.00  
  Purchase #2 $135.55   12.722%   $152.7947   $152.79   $152.80   $152.80  
  Purchase #3 $89.46   9.305%   $97.7843   $97.78   $97.80   $97.80  
  Purchase #4 $207.46   11.350%   $231.0067   $231.01   $231.00   $231.00  
  Purchase #5 $113.40   5.769%   $119.942   $119.94   $119.95   $119.90  
  Purchase #6 $174.39   6.596%   $185.8928   $185.89   $185.90   $185.90  
  Purchase #7 $52.73   11.867%   $58.9875   $58.99   $59.00   $59.00  
  7 purchase totals = $970.40       $1,060.4419   $1,060.43   $1,060.50   $1,060.40