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 $188.95   9.794%   $207.4558   $207.46   $207.45   $207.50  
  Purchase #2 $43.83   5.399%   $46.1964   $46.20   $46.20   $46.20  
  Purchase #3 $60.91   6.738%   $65.0141   $65.01   $65.00   $65.00  
  Purchase #4 $87.58   13.357%   $99.2781   $99.28   $99.30   $99.30  
  Purchase #5 $178.55   7.255%   $191.5038   $191.50   $191.50   $191.50  
  Purchase #6 $43.52   4.824%   $45.6194   $45.62   $45.60   $45.60  
  Purchase #7 $161.51   11.268%   $179.7089   $179.71   $179.70   $179.70  
  7 purchase totals = $764.85       $834.7765   $834.78   $834.75   $834.80