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 $196.73   4.718%   $206.0117   $206.01   $206.00   $206.00  
  Purchase #2 $246.88   8.832%   $268.6844   $268.68   $268.70   $268.70  
  Purchase #3 $33.91   11.566%   $37.832   $37.83   $37.85   $37.80  
  Purchase #4 $163.29   13.570%   $185.4485   $185.45   $185.45   $185.40  
  Purchase #5 $118.30   7.220%   $126.8413   $126.84   $126.85   $126.80  
  Purchase #6 $37.58   4.779%   $39.3759   $39.38   $39.40   $39.40  
  Purchase #7 $34.46   8.183%   $37.2799   $37.28   $37.30   $37.30  
  7 purchase totals = $831.15       $901.4737   $901.47   $901.55   $901.40