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 $196.73   7.542%   $211.5674   $211.57   $211.55   $211.60  
  Purchase #2 $239.59   7.420%   $257.3676   $257.37   $257.35   $257.40  
  Purchase #3 $98.50   5.580%   $103.9963   $104.00   $104.00   $104.00  
  Purchase #4 $150.85   12.596%   $169.8511   $169.85   $169.85   $169.90  
  Purchase #5 $118.34   12.438%   $133.0591   $133.06   $133.05   $133.10  
  Purchase #6 $217.37   10.210%   $239.5635   $239.56   $239.55   $239.60  
  Purchase #7 $23.41   11.523%   $26.1075   $26.11   $26.10   $26.10  
  7 purchase totals = $1,044.79       $1,141.5125   $1,141.52   $1,141.45   $1,141.70