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 $129.59   5.652%   $136.9144   $136.91   $136.90   $136.90  
  Purchase #2 $62.88   6.469%   $66.9477   $66.95   $66.95   $66.90  
  Purchase #3 $224.54   5.571%   $237.0491   $237.05   $237.05   $237.00  
  Purchase #4 $243.86   5.397%   $257.0211   $257.02   $257.00   $257.00  
  Purchase #5 $165.29   4.270%   $172.3479   $172.35   $172.35   $172.30  
  Purchase #6 $16.40   3.797%   $17.0227   $17.02   $17.00   $17.00  
  Purchase #7 $142.30   3.123%   $146.744   $146.74   $146.75   $146.70  
  7 purchase totals = $984.86       $1,034.0469   $1,034.04   $1,034.00   $1,033.80