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 $98.53   7.284%   $105.7069   $105.71   $105.70   $105.70  
  Purchase #2 $96.55   7.164%   $103.4668   $103.47   $103.45   $103.50  
  Purchase #3 $234.64   5.687%   $247.984   $247.98   $248.00   $248.00  
  Purchase #4 $168.88   7.357%   $181.3045   $181.30   $181.30   $181.30  
  Purchase #5 $107.75   5.265%   $113.423   $113.42   $113.40   $113.40  
  Purchase #6 $209.59   12.452%   $235.6881   $235.69   $235.70   $235.70  
  Purchase #7 $54.49   12.180%   $61.1269   $61.13   $61.15   $61.10  
  7 purchase totals = $970.43       $1,048.7002   $1,048.70   $1,048.70   $1,048.70