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 $56.94   6.402%   $60.5853   $60.59   $60.60   $60.60  
  Purchase #2 $75.47   13.383%   $85.5702   $85.57   $85.55   $85.60  
  Purchase #3 $53.31   7.813%   $57.4751   $57.48   $57.50   $57.50  
  Purchase #4 $200.84   12.398%   $225.7401   $225.74   $225.75   $225.70  
  Purchase #5 $210.88   10.838%   $233.7352   $233.74   $233.75   $233.70  
  Purchase #6 $219.26   10.203%   $241.6311   $241.63   $241.65   $241.60  
  Purchase #7 $240.34   12.771%   $271.0338   $271.03   $271.05   $271.00  
  7 purchase totals = $1,057.04       $1,175.7708   $1,175.78   $1,175.85   $1,175.70