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 $174.60   13.857%   $198.7943   $198.79   $198.80   $198.80  
  Purchase #2 $102.80   10.723%   $113.8232   $113.82   $113.80   $113.80  
  Purchase #3 $56.49   4.222%   $58.875   $58.88   $58.90   $58.90  
  Purchase #4 $247.41   3.457%   $255.963   $255.96   $255.95   $256.00  
  Purchase #5 $149.74   10.305%   $165.1707   $165.17   $165.15   $165.20  
  Purchase #6 $123.41   10.195%   $135.9916   $135.99   $136.00   $136.00  
  Purchase #7 $170.27   12.538%   $191.6185   $191.62   $191.60   $191.60  
  7 purchase totals = $1,024.72       $1,120.2363   $1,120.23   $1,120.20   $1,120.30