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 $125.94   6.792%   $134.4938   $134.49   $134.50   $134.50  
  Purchase #2 $7.53   9.205%   $8.2231   $8.22   $8.20   $8.20  
  Purchase #3 $26.92   4.193%   $28.0488   $28.05   $28.05   $28.00  
  Purchase #4 $38.51   8.677%   $41.8515   $41.85   $41.85   $41.90  
  Purchase #5 $196.43   11.526%   $219.0705   $219.07   $219.05   $219.10  
  Purchase #6 $54.98   5.596%   $58.0567   $58.06   $58.05   $58.10  
  Purchase #7 $240.74   3.216%   $248.4822   $248.48   $248.50   $248.50  
  7 purchase totals = $691.05       $738.2266   $738.22   $738.20   $738.30