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 $221.92   13.653%   $252.2187   $252.22   $252.20   $252.20  
  Purchase #2 $136.42   8.369%   $147.837   $147.84   $147.85   $147.80  
  Purchase #3 $54.47   8.312%   $58.9975   $59.00   $59.00   $59.00  
  Purchase #4 $88.85   6.218%   $94.3747   $94.37   $94.35   $94.40  
  Purchase #5 $76.38   9.336%   $83.5108   $83.51   $83.50   $83.50  
  Purchase #6 $217.63   12.806%   $245.4997   $245.50   $245.50   $245.50  
  Purchase #7 $74.89   13.306%   $84.8549   $84.85   $84.85   $84.90  
  7 purchase totals = $870.56       $967.2933   $967.29   $967.25   $967.30