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 $120.90   7.605%   $130.0944   $130.09   $130.10   $130.10  
  Purchase #2 $83.74   4.385%   $87.412   $87.41   $87.40   $87.40  
  Purchase #3 $95.80   9.699%   $105.0916   $105.09   $105.10   $105.10  
  Purchase #4 $190.31   7.537%   $204.6537   $204.65   $204.65   $204.70  
  Purchase #5 $89.46   11.849%   $100.0601   $100.06   $100.05   $100.10  
  Purchase #6 $42.26   10.683%   $46.7746   $46.77   $46.75   $46.80  
  Purchase #7 $7.86   6.272%   $8.353   $8.35   $8.35   $8.40  
  7 purchase totals = $630.33       $682.4394   $682.42   $682.40   $682.60