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 $135.49   8.859%   $147.4931   $147.49   $147.50   $147.50  
  Purchase #2 $233.86   3.198%   $241.3388   $241.34   $241.35   $241.30  
  Purchase #3 $240.68   11.298%   $267.872   $267.87   $267.85   $267.90  
  Purchase #4 $203.79   5.228%   $214.4441   $214.44   $214.45   $214.40  
  Purchase #5 $135.28   11.775%   $151.2092   $151.21   $151.20   $151.20  
  Purchase #6 $202.56   11.640%   $226.138   $226.14   $226.15   $226.10  
  Purchase #7 $10.39   6.844%   $11.1011   $11.10   $11.10   $11.10  
  7 purchase totals = $1,162.05       $1,259.5963   $1,259.59   $1,259.60   $1,259.50