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 $34.74   8.208%   $37.5915   $37.59   $37.60   $37.60  
  Purchase #2 $233.55   13.873%   $265.9504   $265.95   $265.95   $266.00  
  Purchase #3 $23.85   5.647%   $25.1968   $25.20   $25.20   $25.20  
  Purchase #4 $204.75   7.354%   $219.8073   $219.81   $219.80   $219.80  
  Purchase #5 $69.33   11.257%   $77.1345   $77.13   $77.15   $77.10  
  Purchase #6 $168.31   5.126%   $176.9376   $176.94   $176.95   $176.90  
  Purchase #7 $168.54   5.125%   $177.1777   $177.18   $177.20   $177.20  
  7 purchase totals = $903.07       $979.7958   $979.80   $979.85   $979.80