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 $178.62   4.639%   $186.9062   $186.91   $186.90   $186.90  
  Purchase #2 $107.80   9.500%   $118.041   $118.04   $118.05   $118.00  
  Purchase #3 $210.67   13.408%   $238.9166   $238.92   $238.90   $238.90  
  Purchase #4 $200.72   6.151%   $213.0663   $213.07   $213.05   $213.10  
  Purchase #5 $152.44   4.300%   $158.9949   $158.99   $159.00   $159.00  
  Purchase #6 $125.72   9.461%   $137.6144   $137.61   $137.60   $137.60  
  Purchase #7 $30.43   3.734%   $31.5663   $31.57   $31.55   $31.60  
  7 purchase totals = $1,006.40       $1,085.1057   $1,085.11   $1,085.05   $1,085.10