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 $67.27   10.734%   $74.4908   $74.49   $74.50   $74.50  
  Purchase #2 $192.96   10.801%   $213.8016   $213.80   $213.80   $213.80  
  Purchase #3 $157.72   9.443%   $172.6135   $172.61   $172.60   $172.60  
  Purchase #4 $98.43   6.351%   $104.6813   $104.68   $104.70   $104.70  
  Purchase #5 $134.64   10.857%   $149.2579   $149.26   $149.25   $149.30  
  Purchase #6 $70.51   7.356%   $75.6967   $75.70   $75.70   $75.70  
  Purchase #7 $10.58   6.521%   $11.2699   $11.27   $11.25   $11.30  
  7 purchase totals = $732.11       $801.8117   $801.81   $801.80   $801.90