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 $224.66   12.777%   $253.3648   $253.36   $253.35   $253.40  
  Purchase #2 $98.92   8.727%   $107.5527   $107.55   $107.55   $107.60  
  Purchase #3 $207.26   12.160%   $232.4628   $232.46   $232.45   $232.50  
  Purchase #4 $22.96   6.728%   $24.5047   $24.50   $24.50   $24.50  
  Purchase #5 $21.45   6.326%   $22.8069   $22.81   $22.80   $22.80  
  Purchase #6 $151.35   6.512%   $161.2059   $161.21   $161.20   $161.20  
  Purchase #7 $219.37   13.775%   $249.5882   $249.59   $249.60   $249.60  
  7 purchase totals = $945.97       $1,051.4860   $1,051.48   $1,051.45   $1,051.60