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 $28.81   13.145%   $32.5971   $32.60   $32.60   $32.60  
  Purchase #2 $143.89   6.279%   $152.9249   $152.92   $152.90   $152.90  
  Purchase #3 $26.47   12.328%   $29.7332   $29.73   $29.75   $29.70  
  Purchase #4 $170.48   7.779%   $183.7416   $183.74   $183.75   $183.70  
  Purchase #5 $192.53   6.803%   $205.6278   $205.63   $205.65   $205.60  
  Purchase #6 $166.51   6.133%   $176.7221   $176.72   $176.70   $176.70  
  Purchase #7 $222.43   10.393%   $245.5471   $245.55   $245.55   $245.50  
  7 purchase totals = $951.12       $1,026.8938   $1,026.89   $1,026.90   $1,026.70