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 $58.67   3.422%   $60.6777   $60.68   $60.70   $60.70  
  Purchase #2 $165.37   12.838%   $186.6002   $186.60   $186.60   $186.60  
  Purchase #3 $147.94   5.192%   $155.621   $155.62   $155.60   $155.60  
  Purchase #4 $63.63   12.788%   $71.767   $71.77   $71.75   $71.80  
  Purchase #5 $96.80   4.288%   $100.9508   $100.95   $100.95   $101.00  
  Purchase #6 $223.85   5.662%   $236.5244   $236.52   $236.50   $236.50  
  Purchase #7 $15.58   9.172%   $17.009   $17.01   $17.00   $17.00  
  7 purchase totals = $771.84       $829.1501   $829.15   $829.10   $829.20