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 $43.92   11.676%   $49.0481   $49.05   $49.05   $49.00  
  Purchase #2 $240.94   13.370%   $273.1537   $273.15   $273.15   $273.20  
  Purchase #3 $249.86   8.442%   $270.9532   $270.95   $270.95   $271.00  
  Purchase #4 $17.27   10.307%   $19.05   $19.05   $19.05   $19.10  
  Purchase #5 $56.59   7.806%   $61.0074   $61.01   $61.00   $61.00  
  Purchase #6 $209.40   4.873%   $219.6041   $219.60   $219.60   $219.60  
  Purchase #7 $131.30   6.563%   $139.9172   $139.92   $139.90   $139.90  
  7 purchase totals = $949.28       $1,032.7337   $1,032.73   $1,032.70   $1,032.80