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 $62.83   9.722%   $68.9383   $68.94   $68.95   $68.90  
  Purchase #2 $23.46   5.566%   $24.7658   $24.77   $24.75   $24.80  
  Purchase #3 $24.96   11.612%   $27.8584   $27.86   $27.85   $27.90  
  Purchase #4 $32.92   5.623%   $34.7711   $34.77   $34.75   $34.80  
  Purchase #5 $199.31   10.301%   $219.8409   $219.84   $219.85   $219.80  
  Purchase #6 $110.80   4.800%   $116.1184   $116.12   $116.10   $116.10  
  Purchase #7 $244.98   5.813%   $259.2207   $259.22   $259.20   $259.20  
  7 purchase totals = $699.26       $751.5136   $751.52   $751.45   $751.50