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 $112.74   13.360%   $127.8021   $127.80   $127.80   $127.80  
  Purchase #2 $88.29   4.785%   $92.5147   $92.51   $92.50   $92.50  
  Purchase #3 $243.69   8.144%   $263.5361   $263.54   $263.55   $263.50  
  Purchase #4 $204.81   4.765%   $214.5692   $214.57   $214.55   $214.60  
  Purchase #5 $96.42   11.649%   $107.652   $107.65   $107.65   $107.70  
  Purchase #6 $86.37   3.797%   $89.6495   $89.65   $89.65   $89.60  
  Purchase #7 $192.45   11.471%   $214.5259   $214.53   $214.55   $214.50  
  7 purchase totals = $1,024.77       $1,110.2495   $1,110.25   $1,110.25   $1,110.20