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 $34.81   6.219%   $36.9748   $36.97   $36.95   $37.00  
  Purchase #2 $169.41   4.672%   $177.3248   $177.32   $177.30   $177.30  
  Purchase #3 $5.49   5.380%   $5.7854   $5.79   $5.80   $5.80  
  Purchase #4 $33.52   3.253%   $34.6104   $34.61   $34.60   $34.60  
  Purchase #5 $66.63   7.474%   $71.6099   $71.61   $71.60   $71.60  
  Purchase #6 $161.92   4.382%   $169.0153   $169.02   $169.00   $169.00  
  Purchase #7 $231.70   3.449%   $239.6913   $239.69   $239.70   $239.70  
  7 purchase totals = $703.48       $735.0119   $735.01   $734.95   $735.00