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 $196.81   13.512%   $223.403   $223.40   $223.40   $223.40  
  Purchase #2 $210.39   8.589%   $228.4604   $228.46   $228.45   $228.50  
  Purchase #3 $207.69   8.431%   $225.2003   $225.20   $225.20   $225.20  
  Purchase #4 $188.85   9.518%   $206.8247   $206.82   $206.80   $206.80  
  Purchase #5 $47.33   6.667%   $50.4855   $50.49   $50.50   $50.50  
  Purchase #6 $25.76   10.572%   $28.4833   $28.48   $28.50   $28.50  
  Purchase #7 $183.55   10.199%   $202.2703   $202.27   $202.25   $202.30  
  7 purchase totals = $1,060.38       $1,165.1275   $1,165.12   $1,165.10   $1,165.20