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 $68.46   11.734%   $76.4931   $76.49   $76.50   $76.50  
  Purchase #2 $185.91   9.774%   $204.0808   $204.08   $204.10   $204.10  
  Purchase #3 $201.96   4.840%   $211.7349   $211.73   $211.75   $211.70  
  Purchase #4 $61.54   12.644%   $69.3211   $69.32   $69.30   $69.30  
  Purchase #5 $8.79   8.193%   $9.5102   $9.51   $9.50   $9.50  
  Purchase #6 $69.67   13.748%   $79.2482   $79.25   $79.25   $79.20  
  Purchase #7 $239.25   13.623%   $271.843   $271.84   $271.85   $271.80  
  7 purchase totals = $835.58       $922.2313   $922.22   $922.25   $922.10