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 $23.30   7.362%   $25.0153   $25.02   $25.00   $25.00  
  Purchase #2 $200.82   5.171%   $211.2044   $211.20   $211.20   $211.20  
  Purchase #3 $151.70   13.805%   $172.6422   $172.64   $172.65   $172.60  
  Purchase #4 $133.97   8.633%   $145.5356   $145.54   $145.55   $145.50  
  Purchase #5 $26.95   7.554%   $28.9858   $28.99   $29.00   $29.00  
  Purchase #6 $89.84   10.197%   $99.001   $99.00   $99.00   $99.00  
  Purchase #7 $240.94   7.848%   $259.849   $259.85   $259.85   $259.80  
  7 purchase totals = $867.52       $942.2333   $942.24   $942.25   $942.10