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 $24.31   5.529%   $25.6541   $25.65   $25.65   $25.70  
  Purchase #2 $160.64   5.240%   $169.0575   $169.06   $169.05   $169.10  
  Purchase #3 $58.27   6.456%   $62.0319   $62.03   $62.05   $62.00  
  Purchase #4 $137.59   11.134%   $152.9093   $152.91   $152.90   $152.90  
  Purchase #5 $36.63   6.622%   $39.0556   $39.06   $39.05   $39.10  
  Purchase #6 $151.96   7.703%   $163.6655   $163.67   $163.65   $163.70  
  Purchase #7 $144.96   10.832%   $160.6621   $160.66   $160.65   $160.70  
  7 purchase totals = $714.36       $773.0360   $773.04   $773.00   $773.20