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 $78.74   10.820%   $87.2597   $87.26   $87.25   $87.30  
  Purchase #2 $37.26   13.593%   $42.3248   $42.32   $42.30   $42.30  
  Purchase #3 $174.37   4.859%   $182.8426   $182.84   $182.85   $182.80  
  Purchase #4 $126.58   12.160%   $141.9721   $141.97   $141.95   $142.00  
  Purchase #5 $185.52   6.747%   $198.037   $198.04   $198.05   $198.00  
  Purchase #6 $201.49   12.122%   $225.9146   $225.91   $225.90   $225.90  
  Purchase #7 $185.61   11.747%   $207.4136   $207.41   $207.40   $207.40  
  7 purchase totals = $989.57       $1,085.7644   $1,085.75   $1,085.70   $1,085.70