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 $176.61   10.793%   $195.6715   $195.67   $195.65   $195.70  
  Purchase #2 $175.49   9.815%   $192.7143   $192.71   $192.70   $192.70  
  Purchase #3 $137.53   5.849%   $145.5741   $145.57   $145.55   $145.60  
  Purchase #4 $206.45   4.446%   $215.6288   $215.63   $215.65   $215.60  
  Purchase #5 $179.42   11.712%   $200.4337   $200.43   $200.45   $200.40  
  Purchase #6 $227.74   10.481%   $251.6094   $251.61   $251.60   $251.60  
  Purchase #7 $69.80   7.349%   $74.9296   $74.93   $74.95   $74.90  
  7 purchase totals = $1,173.04       $1,276.5614   $1,276.55   $1,276.55   $1,276.50