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 $63.48   8.596%   $68.9367   $68.94   $68.95   $68.90  
  Purchase #2 $58.94   8.463%   $63.9281   $63.93   $63.95   $63.90  
  Purchase #3 $68.43   3.751%   $70.9968   $71.00   $71.00   $71.00  
  Purchase #4 $120.46   5.168%   $126.6854   $126.69   $126.70   $126.70  
  Purchase #5 $49.36   4.655%   $51.6577   $51.66   $51.65   $51.70  
  Purchase #6 $199.49   7.177%   $213.8074   $213.81   $213.80   $213.80  
  Purchase #7 $31.86   6.650%   $33.9787   $33.98   $34.00   $34.00  
  7 purchase totals = $592.02       $629.9908   $630.01   $630.05   $630.00