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 $57.83   7.246%   $62.0204   $62.02   $62.00   $62.00  
  Purchase #2 $217.98   3.201%   $224.9575   $224.96   $224.95   $225.00  
  Purchase #3 $213.31   5.613%   $225.2831   $225.28   $225.30   $225.30  
  Purchase #4 $113.59   5.629%   $119.984   $119.98   $120.00   $120.00  
  Purchase #5 $176.25   9.198%   $192.4615   $192.46   $192.45   $192.50  
  Purchase #6 $106.55   11.652%   $118.9652   $118.97   $118.95   $119.00  
  Purchase #7 $61.90   3.595%   $64.1253   $64.13   $64.15   $64.10  
  7 purchase totals = $947.41       $1,007.7970   $1,007.80   $1,007.80   $1,007.90