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 $177.96   4.506%   $185.9789   $185.98   $186.00   $186.00  
  Purchase #2 $86.86   10.434%   $95.923   $95.92   $95.90   $95.90  
  Purchase #3 $227.83   12.415%   $256.1151   $256.12   $256.10   $256.10  
  Purchase #4 $213.25   9.530%   $233.5727   $233.57   $233.55   $233.60  
  Purchase #5 $102.43   4.225%   $106.7577   $106.76   $106.75   $106.80  
  Purchase #6 $52.90   8.629%   $57.4647   $57.46   $57.45   $57.50  
  Purchase #7 $246.56   6.341%   $262.1944   $262.19   $262.20   $262.20  
  7 purchase totals = $1,107.79       $1,198.0065   $1,198.00   $1,197.95   $1,198.10