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 $91.59   6.723%   $97.7476   $97.75   $97.75   $97.70  
  Purchase #2 $8.34   3.717%   $8.65   $8.65   $8.65   $8.70  
  Purchase #3 $20.90   10.299%   $23.0525   $23.05   $23.05   $23.10  
  Purchase #4 $174.32   5.680%   $184.2214   $184.22   $184.20   $184.20  
  Purchase #5 $80.61   10.422%   $89.0112   $89.01   $89.00   $89.00  
  Purchase #6 $54.34   6.371%   $57.802   $57.80   $57.80   $57.80  
  Purchase #7 $207.53   3.570%   $214.9388   $214.94   $214.95   $214.90  
  7 purchase totals = $637.63       $675.4235   $675.42   $675.40   $675.40