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 $206.88   11.743%   $231.1739   $231.17   $231.15   $231.20  
  Purchase #2 $188.66   5.693%   $199.4004   $199.40   $199.40   $199.40  
  Purchase #3 $161.77   12.774%   $182.4345   $182.43   $182.45   $182.40  
  Purchase #4 $14.74   5.722%   $15.5834   $15.58   $15.60   $15.60  
  Purchase #5 $159.28   8.668%   $173.0864   $173.09   $173.10   $173.10  
  Purchase #6 $58.55   6.433%   $62.3165   $62.32   $62.30   $62.30  
  Purchase #7 $193.89   5.214%   $203.9994   $204.00   $204.00   $204.00  
  7 purchase totals = $983.77       $1,067.9945   $1,067.99   $1,068.00   $1,068.00