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 $183.92   5.242%   $193.5611   $193.56   $193.55   $193.60  
  Purchase #2 $124.49   12.250%   $139.74   $139.74   $139.75   $139.70  
  Purchase #3 $128.58   5.483%   $135.63   $135.63   $135.65   $135.60  
  Purchase #4 $66.35   11.413%   $73.9225   $73.92   $73.90   $73.90  
  Purchase #5 $140.47   5.492%   $148.1846   $148.18   $148.20   $148.20  
  Purchase #6 $118.79   5.269%   $125.049   $125.05   $125.05   $125.00  
  Purchase #7 $198.26   3.687%   $205.5698   $205.57   $205.55   $205.60  
  7 purchase totals = $960.86       $1,021.6570   $1,021.65   $1,021.65   $1,021.60