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 $57.40   13.665%   $65.2437   $65.24   $65.25   $65.20  
  Purchase #2 $93.64   9.568%   $102.5995   $102.60   $102.60   $102.60  
  Purchase #3 $34.44   4.409%   $35.9585   $35.96   $35.95   $36.00  
  Purchase #4 $214.75   6.372%   $228.4339   $228.43   $228.45   $228.40  
  Purchase #5 $58.33   7.290%   $62.5823   $62.58   $62.60   $62.60  
  Purchase #6 $195.62   10.321%   $215.8099   $215.81   $215.80   $215.80  
  Purchase #7 $120.29   3.749%   $124.7997   $124.80   $124.80   $124.80  
  7 purchase totals = $774.47       $835.4275   $835.42   $835.45   $835.40