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 $206.61   5.871%   $218.7401   $218.74   $218.75   $218.70  
  Purchase #2 $190.85   9.324%   $208.6449   $208.64   $208.65   $208.60  
  Purchase #3 $132.52   6.634%   $141.3114   $141.31   $141.30   $141.30  
  Purchase #4 $77.60   5.257%   $81.6794   $81.68   $81.70   $81.70  
  Purchase #5 $68.34   6.824%   $73.0035   $73.00   $73.00   $73.00  
  Purchase #6 $100.25   3.731%   $103.9903   $103.99   $104.00   $104.00  
  Purchase #7 $237.36   7.675%   $255.5774   $255.58   $255.60   $255.60  
  7 purchase totals = $1,013.53       $1,082.9470   $1,082.94   $1,083.00   $1,082.90