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 $174.53   12.267%   $195.9396   $195.94   $195.95   $195.90  
  Purchase #2 $124.62   11.178%   $138.55   $138.55   $138.55   $138.60  
  Purchase #3 $72.51   7.225%   $77.7488   $77.75   $77.75   $77.70  
  Purchase #4 $162.69   10.316%   $179.4731   $179.47   $179.45   $179.50  
  Purchase #5 $162.85   12.260%   $182.8154   $182.82   $182.80   $182.80  
  Purchase #6 $89.44   5.466%   $94.3288   $94.33   $94.35   $94.30  
  Purchase #7 $27.60   12.188%   $30.9639   $30.96   $30.95   $31.00  
  7 purchase totals = $814.24       $899.8196   $899.82   $899.80   $899.80