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 $107.97   10.781%   $119.6102   $119.61   $119.60   $119.60  
  Purchase #2 $35.30   3.874%   $36.6675   $36.67   $36.65   $36.70  
  Purchase #3 $207.43   11.129%   $230.5149   $230.51   $230.50   $230.50  
  Purchase #4 $193.58   10.732%   $214.355   $214.36   $214.35   $214.40  
  Purchase #5 $102.75   3.413%   $106.2569   $106.26   $106.25   $106.30  
  Purchase #6 $43.54   11.360%   $48.4861   $48.49   $48.50   $48.50  
  Purchase #7 $134.71   10.478%   $148.8249   $148.82   $148.80   $148.80  
  7 purchase totals = $825.28       $904.7155   $904.72   $904.65   $904.80