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 $218.91   12.361%   $245.9695   $245.97   $245.95   $246.00  
  Purchase #2 $72.84   13.822%   $82.9079   $82.91   $82.90   $82.90  
  Purchase #3 $179.55   8.322%   $194.4922   $194.49   $194.50   $194.50  
  Purchase #4 $66.73   10.279%   $73.5892   $73.59   $73.60   $73.60  
  Purchase #5 $79.74   10.336%   $87.9819   $87.98   $88.00   $88.00  
  Purchase #6 $96.83   5.383%   $102.0424   $102.04   $102.05   $102.00  
  Purchase #7 $5.33   13.563%   $6.0529   $6.05   $6.05   $6.10  
  7 purchase totals = $719.93       $793.0360   $793.03   $793.05   $793.10