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 $222.35   5.380%   $234.3124   $234.31   $234.30   $234.30  
  Purchase #2 $86.61   9.199%   $94.5773   $94.58   $94.60   $94.60  
  Purchase #3 $29.62   13.257%   $33.5467   $33.55   $33.55   $33.50  
  Purchase #4 $50.68   5.418%   $53.4258   $53.43   $53.45   $53.40  
  Purchase #5 $199.92   9.267%   $218.4466   $218.45   $218.45   $218.40  
  Purchase #6 $105.40   11.577%   $117.6022   $117.60   $117.60   $117.60  
  Purchase #7 $231.69   13.386%   $262.704   $262.70   $262.70   $262.70  
  7 purchase totals = $926.27       $1,014.6150   $1,014.62   $1,014.65   $1,014.50