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 $84.97   13.198%   $96.1843   $96.18   $96.20   $96.20  
  Purchase #2 $105.39   3.137%   $108.6961   $108.70   $108.70   $108.70  
  Purchase #3 $140.35   9.850%   $154.1745   $154.17   $154.15   $154.20  
  Purchase #4 $41.85   13.212%   $47.3792   $47.38   $47.40   $47.40  
  Purchase #5 $120.80   12.851%   $136.324   $136.32   $136.30   $136.30  
  Purchase #6 $171.82   12.241%   $192.8525   $192.85   $192.85   $192.90  
  Purchase #7 $16.32   7.740%   $17.5832   $17.58   $17.60   $17.60  
  7 purchase totals = $681.50       $753.1938   $753.18   $753.20   $753.30