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 $61.48   13.423%   $69.7325   $69.73   $69.75   $69.70  
  Purchase #2 $212.61   13.216%   $240.7085   $240.71   $240.70   $240.70  
  Purchase #3 $85.78   9.679%   $94.0826   $94.08   $94.10   $94.10  
  Purchase #4 $17.94   12.112%   $20.1129   $20.11   $20.10   $20.10  
  Purchase #5 $60.32   12.664%   $67.9589   $67.96   $67.95   $68.00  
  Purchase #6 $182.96   5.520%   $193.0594   $193.06   $193.05   $193.10  
  Purchase #7 $135.65   4.152%   $141.2822   $141.28   $141.30   $141.30  
  7 purchase totals = $756.74       $826.9370   $826.93   $826.95   $827.00