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 $90.25   8.253%   $97.6983   $97.70   $97.70   $97.70  
  Purchase #2 $234.91   10.331%   $259.1786   $259.18   $259.20   $259.20  
  Purchase #3 $55.72   8.544%   $60.4807   $60.48   $60.50   $60.50  
  Purchase #4 $244.49   13.821%   $278.281   $278.28   $278.30   $278.30  
  Purchase #5 $224.77   10.182%   $247.6561   $247.66   $247.65   $247.70  
  Purchase #6 $158.93   3.342%   $164.2414   $164.24   $164.25   $164.20  
  Purchase #7 $184.29   9.164%   $201.1783   $201.18   $201.20   $201.20  
  7 purchase totals = $1,193.36       $1,308.7144   $1,308.72   $1,308.80   $1,308.80