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 $125.43   4.649%   $131.2612   $131.26   $131.25   $131.30  
  Purchase #2 $209.55   9.589%   $229.6437   $229.64   $229.65   $229.60  
  Purchase #3 $191.88   9.242%   $209.6135   $209.61   $209.60   $209.60  
  Purchase #4 $151.85   12.873%   $171.3977   $171.40   $171.40   $171.40  
  Purchase #5 $29.57   13.676%   $33.614   $33.61   $33.60   $33.60  
  Purchase #6 $106.73   12.499%   $120.0702   $120.07   $120.05   $120.10  
  Purchase #7 $133.79   4.305%   $139.5497   $139.55   $139.55   $139.50  
  7 purchase totals = $948.80       $1,035.1500   $1,035.14   $1,035.10   $1,035.10