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 $135.99   13.627%   $154.5214   $154.52   $154.50   $154.50  
  Purchase #2 $206.89   10.653%   $228.93   $228.93   $228.95   $228.90  
  Purchase #3 $208.93   3.459%   $216.1569   $216.16   $216.15   $216.20  
  Purchase #4 $250.78   9.316%   $274.1427   $274.14   $274.15   $274.10  
  Purchase #5 $64.51   8.160%   $69.774   $69.77   $69.75   $69.80  
  Purchase #6 $75.47   13.836%   $85.912   $85.91   $85.90   $85.90  
  Purchase #7 $232.97   5.683%   $246.2097   $246.21   $246.20   $246.20  
  7 purchase totals = $1,175.54       $1,275.6467   $1,275.64   $1,275.60   $1,275.60