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 $39.45   9.432%   $43.1709   $43.17   $43.15   $43.20  
  Purchase #2 $246.83   8.478%   $267.7562   $267.76   $267.75   $267.80  
  Purchase #3 $146.35   3.868%   $152.0108   $152.01   $152.00   $152.00  
  Purchase #4 $189.92   8.698%   $206.4392   $206.44   $206.45   $206.40  
  Purchase #5 $61.71   11.742%   $68.956   $68.96   $68.95   $69.00  
  Purchase #6 $149.44   8.463%   $162.0871   $162.09   $162.10   $162.10  
  Purchase #7 $164.82   4.216%   $171.7688   $171.77   $171.75   $171.80  
  7 purchase totals = $998.52       $1,072.1890   $1,072.20   $1,072.15   $1,072.30