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 $222.51   10.606%   $246.1094   $246.11   $246.10   $246.10  
  Purchase #2 $159.86   9.356%   $174.8165   $174.82   $174.80   $174.80  
  Purchase #3 $30.90   7.114%   $33.0982   $33.10   $33.10   $33.10  
  Purchase #4 $223.28   13.426%   $253.2576   $253.26   $253.25   $253.30  
  Purchase #5 $32.81   12.811%   $37.0133   $37.01   $37.00   $37.00  
  Purchase #6 $246.64   12.448%   $277.3417   $277.34   $277.35   $277.30  
  Purchase #7 $246.28   11.160%   $273.7648   $273.76   $273.75   $273.80  
  7 purchase totals = $1,162.28       $1,295.4015   $1,295.40   $1,295.35   $1,295.40