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 $154.87   13.227%   $175.3547   $175.35   $175.35   $175.40  
  Purchase #2 $63.25   4.246%   $65.9356   $65.94   $65.95   $65.90  
  Purchase #3 $59.89   8.496%   $64.9783   $64.98   $65.00   $65.00  
  Purchase #4 $68.58   13.639%   $77.9336   $77.93   $77.95   $77.90  
  Purchase #5 $239.88   13.143%   $271.4074   $271.41   $271.40   $271.40  
  Purchase #6 $169.34   13.793%   $192.6971   $192.70   $192.70   $192.70  
  Purchase #7 $181.70   5.658%   $191.9806   $191.98   $192.00   $192.00  
  7 purchase totals = $937.51       $1,040.2873   $1,040.29   $1,040.35   $1,040.30