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 $146.35   6.766%   $156.252   $156.25   $156.25   $156.30  
  Purchase #2 $114.84   4.703%   $120.2409   $120.24   $120.25   $120.20  
  Purchase #3 $223.45   3.255%   $230.7233   $230.72   $230.70   $230.70  
  Purchase #4 $104.37   13.157%   $118.102   $118.10   $118.10   $118.10  
  Purchase #5 $27.50   6.312%   $29.2358   $29.24   $29.25   $29.20  
  Purchase #6 $10.58   6.300%   $11.2465   $11.25   $11.25   $11.20  
  Purchase #7 $61.37   9.467%   $67.1799   $67.18   $67.20   $67.20  
  7 purchase totals = $688.46       $732.9804   $732.98   $733.00   $732.90