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 $68.49   8.284%   $74.1637   $74.16   $74.15   $74.20  
  Purchase #2 $55.25   10.310%   $60.9463   $60.95   $60.95   $60.90  
  Purchase #3 $163.85   3.825%   $170.1173   $170.12   $170.10   $170.10  
  Purchase #4 $89.40   11.138%   $99.3574   $99.36   $99.35   $99.40  
  Purchase #5 $178.28   4.103%   $185.5948   $185.59   $185.60   $185.60  
  Purchase #6 $25.34   4.633%   $26.514   $26.51   $26.50   $26.50  
  Purchase #7 $193.37   9.161%   $211.0846   $211.08   $211.10   $211.10  
  7 purchase totals = $773.98       $827.7781   $827.77   $827.75   $827.80