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 $163.65   13.782%   $186.2042   $186.20   $186.20   $186.20  
  Purchase #2 $82.39   6.645%   $87.8648   $87.86   $87.85   $87.90  
  Purchase #3 $120.25   4.463%   $125.6168   $125.62   $125.60   $125.60  
  Purchase #4 $131.50   10.603%   $145.4429   $145.44   $145.45   $145.40  
  Purchase #5 $238.57   10.474%   $263.5578   $263.56   $263.55   $263.60  
  Purchase #6 $187.49   10.847%   $207.827   $207.83   $207.85   $207.80  
  Purchase #7 $210.37   13.644%   $239.0729   $239.07   $239.05   $239.10  
  7 purchase totals = $1,134.22       $1,255.5864   $1,255.58   $1,255.55   $1,255.60