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 $125.73   8.689%   $136.6547   $136.65   $136.65   $136.70  
  Purchase #2 $225.51   3.555%   $233.5269   $233.53   $233.55   $233.50  
  Purchase #3 $78.34   8.423%   $84.9386   $84.94   $84.95   $84.90  
  Purchase #4 $204.65   7.124%   $219.2293   $219.23   $219.25   $219.20  
  Purchase #5 $203.93   11.775%   $227.9428   $227.94   $227.95   $227.90  
  Purchase #6 $132.30   8.156%   $143.0904   $143.09   $143.10   $143.10  
  Purchase #7 $148.86   11.297%   $165.6767   $165.68   $165.70   $165.70  
  7 purchase totals = $1,119.32       $1,211.0594   $1,211.06   $1,211.15   $1,211.00