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 $147.47   12.301%   $165.6103   $165.61   $165.60   $165.60  
  Purchase #2 $36.63   13.446%   $41.5553   $41.56   $41.55   $41.60  
  Purchase #3 $182.94   7.851%   $197.3026   $197.30   $197.30   $197.30  
  Purchase #4 $5.64   4.207%   $5.8773   $5.88   $5.90   $5.90  
  Purchase #5 $63.66   6.779%   $67.9755   $67.98   $68.00   $68.00  
  Purchase #6 $79.46   4.729%   $83.2177   $83.22   $83.20   $83.20  
  Purchase #7 $157.75   10.300%   $173.9983   $174.00   $174.00   $174.00  
  7 purchase totals = $673.55       $735.5370   $735.55   $735.55   $735.60