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 $89.35   7.337%   $95.9056   $95.91   $95.90   $95.90  
  Purchase #2 $232.84   13.378%   $263.9893   $263.99   $264.00   $264.00  
  Purchase #3 $213.91   11.674%   $238.8819   $238.88   $238.90   $238.90  
  Purchase #4 $93.87   7.544%   $100.9516   $100.95   $100.95   $101.00  
  Purchase #5 $239.60   8.244%   $259.3526   $259.35   $259.35   $259.40  
  Purchase #6 $213.95   12.408%   $240.4969   $240.50   $240.50   $240.50  
  Purchase #7 $219.60   12.589%   $247.2454   $247.25   $247.25   $247.20  
  7 purchase totals = $1,303.12       $1,446.8233   $1,446.83   $1,446.85   $1,446.90