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 $226.29   3.840%   $234.9795   $234.98   $235.00   $235.00  
  Purchase #2 $126.74   12.812%   $142.9779   $142.98   $143.00   $143.00  
  Purchase #3 $248.72   6.695%   $265.3718   $265.37   $265.35   $265.40  
  Purchase #4 $185.98   9.620%   $203.8713   $203.87   $203.85   $203.90  
  Purchase #5 $233.91   5.291%   $246.2862   $246.29   $246.30   $246.30  
  Purchase #6 $105.36   12.683%   $118.7228   $118.72   $118.70   $118.70  
  Purchase #7 $73.71   6.777%   $78.7053   $78.71   $78.70   $78.70  
  7 purchase totals = $1,200.71       $1,290.9148   $1,290.92   $1,290.90   $1,291.00