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 $126.44   5.621%   $133.5472   $133.55   $133.55   $133.50  
  Purchase #2 $161.63   10.415%   $178.4638   $178.46   $178.45   $178.50  
  Purchase #3 $219.43   10.198%   $241.8075   $241.81   $241.80   $241.80  
  Purchase #4 $163.28   8.283%   $176.8045   $176.80   $176.80   $176.80  
  Purchase #5 $48.53   13.768%   $55.2116   $55.21   $55.20   $55.20  
  Purchase #6 $202.64   4.838%   $212.4437   $212.44   $212.45   $212.40  
  Purchase #7 $57.27   11.323%   $63.7547   $63.75   $63.75   $63.80  
  7 purchase totals = $979.22       $1,062.0330   $1,062.02   $1,062.00   $1,062.00