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 $60.61   11.274%   $67.4432   $67.44   $67.45   $67.40  
  Purchase #2 $176.28   8.709%   $191.6322   $191.63   $191.65   $191.60  
  Purchase #3 $165.97   6.702%   $177.0933   $177.09   $177.10   $177.10  
  Purchase #4 $149.83   7.687%   $161.3474   $161.35   $161.35   $161.30  
  Purchase #5 $55.92   9.369%   $61.1591   $61.16   $61.15   $61.20  
  Purchase #6 $100.31   8.601%   $108.9377   $108.94   $108.95   $108.90  
  Purchase #7 $94.91   6.415%   $100.9985   $101.00   $101.00   $101.00  
  7 purchase totals = $803.83       $868.6114   $868.61   $868.65   $868.50