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 $204.86   4.157%   $213.376   $213.38   $213.40   $213.40  
  Purchase #2 $37.25   3.367%   $38.5042   $38.50   $38.50   $38.50  
  Purchase #3 $159.94   6.705%   $170.664   $170.66   $170.65   $170.70  
  Purchase #4 $42.96   9.367%   $46.9841   $46.98   $47.00   $47.00  
  Purchase #5 $134.43   3.102%   $138.6   $138.60   $138.60   $138.60  
  Purchase #6 $166.94   8.572%   $181.2501   $181.25   $181.25   $181.30  
  Purchase #7 $213.69   5.778%   $226.037   $226.04   $226.05   $226.00  
  7 purchase totals = $960.07       $1,015.4154   $1,015.41   $1,015.45   $1,015.50