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 $54.37   8.605%   $59.0485   $59.05   $59.05   $59.00  
  Purchase #2 $118.74   12.574%   $133.6704   $133.67   $133.65   $133.70  
  Purchase #3 $17.32   8.340%   $18.7645   $18.76   $18.75   $18.80  
  Purchase #4 $129.92   9.799%   $142.6509   $142.65   $142.65   $142.70  
  Purchase #5 $175.30   10.185%   $193.1543   $193.15   $193.15   $193.20  
  Purchase #6 $93.87   6.247%   $99.7341   $99.73   $99.75   $99.70  
  Purchase #7 $37.37   6.824%   $39.9201   $39.92   $39.90   $39.90  
  7 purchase totals = $626.89       $686.9428   $686.93   $686.90   $687.00