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 $133.78   6.136%   $141.9887   $141.99   $142.00   $142.00  
  Purchase #2 $140.80   8.846%   $153.2552   $153.26   $153.25   $153.30  
  Purchase #3 $87.29   8.787%   $94.9602   $94.96   $94.95   $95.00  
  Purchase #4 $56.27   12.436%   $63.2677   $63.27   $63.25   $63.30  
  Purchase #5 $247.88   13.786%   $282.0527   $282.05   $282.05   $282.10  
  Purchase #6 $82.49   5.167%   $86.7523   $86.75   $86.75   $86.80  
  Purchase #7 $215.64   6.748%   $230.1914   $230.19   $230.20   $230.20  
  7 purchase totals = $964.15       $1,052.4682   $1,052.47   $1,052.45   $1,052.70