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 $62.96   5.818%   $66.623   $66.62   $66.60   $66.60  
  Purchase #2 $201.58   3.196%   $208.0225   $208.02   $208.00   $208.00  
  Purchase #3 $225.33   5.260%   $237.1824   $237.18   $237.20   $237.20  
  Purchase #4 $24.72   6.692%   $26.3743   $26.37   $26.35   $26.40  
  Purchase #5 $91.31   6.362%   $97.1191   $97.12   $97.10   $97.10  
  Purchase #6 $53.61   8.641%   $58.2424   $58.24   $58.25   $58.20  
  Purchase #7 $247.48   10.743%   $274.0668   $274.07   $274.05   $274.10  
  7 purchase totals = $906.99       $967.6305   $967.62   $967.55   $967.60