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 $177.49   5.166%   $186.6591   $186.66   $186.65   $186.70  
  Purchase #2 $181.33   6.381%   $192.9007   $192.90   $192.90   $192.90  
  Purchase #3 $91.93   12.580%   $103.4948   $103.49   $103.50   $103.50  
  Purchase #4 $214.41   4.827%   $224.7596   $224.76   $224.75   $224.80  
  Purchase #5 $205.36   12.734%   $231.5105   $231.51   $231.50   $231.50  
  Purchase #6 $203.81   6.429%   $216.9129   $216.91   $216.90   $216.90  
  Purchase #7 $239.91   13.220%   $271.6261   $271.63   $271.65   $271.60  
  7 purchase totals = $1,314.24       $1,427.8637   $1,427.86   $1,427.85   $1,427.90