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 $98.41   4.720%   $103.055   $103.06   $103.05   $103.10  
  Purchase #2 $110.49   13.684%   $125.6095   $125.61   $125.60   $125.60  
  Purchase #3 $166.72   4.673%   $174.5108   $174.51   $174.50   $174.50  
  Purchase #4 $81.97   3.556%   $84.8849   $84.88   $84.90   $84.90  
  Purchase #5 $74.55   6.424%   $79.3391   $79.34   $79.35   $79.30  
  Purchase #6 $89.39   7.380%   $95.987   $95.99   $96.00   $96.00  
  Purchase #7 $126.73   5.689%   $133.9397   $133.94   $133.95   $133.90  
  7 purchase totals = $748.26       $797.3260   $797.33   $797.35   $797.30