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 $216.90   13.790%   $246.8105   $246.81   $246.80   $246.80  
  Purchase #2 $190.85   11.864%   $213.4924   $213.49   $213.50   $213.50  
  Purchase #3 $127.39   12.841%   $143.7481   $143.75   $143.75   $143.70  
  Purchase #4 $47.97   10.212%   $52.8687   $52.87   $52.85   $52.90  
  Purchase #5 $23.88   6.330%   $25.3916   $25.39   $25.40   $25.40  
  Purchase #6 $231.64   6.776%   $247.3359   $247.34   $247.35   $247.30  
  Purchase #7 $170.32   6.671%   $181.682   $181.68   $181.70   $181.70  
  7 purchase totals = $1,008.95       $1,111.3292   $1,111.33   $1,111.35   $1,111.30