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 $243.43   8.847%   $264.9663   $264.97   $264.95   $265.00  
  Purchase #2 $212.40   8.693%   $230.8639   $230.86   $230.85   $230.90  
  Purchase #3 $61.85   5.444%   $65.2171   $65.22   $65.20   $65.20  
  Purchase #4 $9.51   3.868%   $9.8778   $9.88   $9.90   $9.90  
  Purchase #5 $104.54   12.753%   $117.872   $117.87   $117.85   $117.90  
  Purchase #6 $130.54   13.769%   $148.5141   $148.51   $148.50   $148.50  
  Purchase #7 $103.76   4.351%   $108.2746   $108.27   $108.25   $108.30  
  7 purchase totals = $866.03       $945.5858   $945.58   $945.50   $945.70