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 $61.87   9.233%   $67.5825   $67.58   $67.60   $67.60  
  Purchase #2 $93.26   12.689%   $105.0938   $105.09   $105.10   $105.10  
  Purchase #3 $47.34   9.427%   $51.8027   $51.80   $51.80   $51.80  
  Purchase #4 $101.29   9.156%   $110.5641   $110.56   $110.55   $110.60  
  Purchase #5 $241.87   13.546%   $274.6337   $274.63   $274.65   $274.60  
  Purchase #6 $137.28   7.250%   $147.2328   $147.23   $147.25   $147.20  
  Purchase #7 $220.96   9.309%   $241.5292   $241.53   $241.55   $241.50  
  7 purchase totals = $903.87       $998.4388   $998.42   $998.50   $998.40