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 $162.49   10.314%   $179.2492   $179.25   $179.25   $179.20  
  Purchase #2 $224.79   8.256%   $243.3487   $243.35   $243.35   $243.30  
  Purchase #3 $196.92   11.264%   $219.1011   $219.10   $219.10   $219.10  
  Purchase #4 $241.58   3.323%   $249.6077   $249.61   $249.60   $249.60  
  Purchase #5 $91.90   9.498%   $100.6287   $100.63   $100.65   $100.60  
  Purchase #6 $183.81   12.637%   $207.0381   $207.04   $207.05   $207.00  
  Purchase #7 $130.35   11.864%   $145.8147   $145.81   $145.80   $145.80  
  7 purchase totals = $1,231.84       $1,344.7882   $1,344.79   $1,344.80   $1,344.60