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 $237.59   6.298%   $252.5534   $252.55   $252.55   $252.60  
  Purchase #2 $58.51   7.683%   $63.0053   $63.01   $63.00   $63.00  
  Purchase #3 $89.95   5.787%   $95.1554   $95.16   $95.15   $95.20  
  Purchase #4 $241.75   6.359%   $257.1229   $257.12   $257.10   $257.10  
  Purchase #5 $137.84   11.340%   $153.4711   $153.47   $153.45   $153.50  
  Purchase #6 $149.51   9.502%   $163.7164   $163.72   $163.70   $163.70  
  Purchase #7 $194.56   11.680%   $217.2846   $217.28   $217.30   $217.30  
  7 purchase totals = $1,109.71       $1,202.3091   $1,202.31   $1,202.25   $1,202.40