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 $224.51   8.155%   $242.8188   $242.82   $242.80   $242.80  
  Purchase #2 $243.35   7.702%   $262.0928   $262.09   $262.10   $262.10  
  Purchase #3 $40.29   8.478%   $43.7058   $43.71   $43.70   $43.70  
  Purchase #4 $195.61   5.820%   $206.9945   $206.99   $207.00   $207.00  
  Purchase #5 $102.76   6.137%   $109.0664   $109.07   $109.05   $109.10  
  Purchase #6 $166.26   9.437%   $181.95   $181.95   $181.95   $182.00  
  Purchase #7 $23.38   5.579%   $24.6844   $24.68   $24.70   $24.70  
  7 purchase totals = $996.16       $1,071.3127   $1,071.31   $1,071.30   $1,071.40