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 $211.93   13.796%   $241.1679   $241.17   $241.15   $241.20  
  Purchase #2 $231.87   11.256%   $257.9693   $257.97   $257.95   $258.00  
  Purchase #3 $110.40   7.629%   $118.8224   $118.82   $118.80   $118.80  
  Purchase #4 $219.30   7.204%   $235.0984   $235.10   $235.10   $235.10  
  Purchase #5 $247.44   4.560%   $258.7233   $258.72   $258.70   $258.70  
  Purchase #6 $44.43   3.610%   $46.0339   $46.03   $46.05   $46.00  
  Purchase #7 $113.28   12.679%   $127.6428   $127.64   $127.65   $127.60  
  7 purchase totals = $1,178.65       $1,285.4580   $1,285.45   $1,285.40   $1,285.40