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 $184.49   10.377%   $203.6345   $203.63   $203.65   $203.60  
  Purchase #2 $168.99   12.793%   $190.6089   $190.61   $190.60   $190.60  
  Purchase #3 $149.34   4.531%   $156.1066   $156.11   $156.10   $156.10  
  Purchase #4 $123.77   4.556%   $129.409   $129.41   $129.40   $129.40  
  Purchase #5 $218.28   6.387%   $232.2215   $232.22   $232.20   $232.20  
  Purchase #6 $87.33   6.386%   $92.9069   $92.91   $92.90   $92.90  
  Purchase #7 $21.95   10.764%   $24.3127   $24.31   $24.30   $24.30  
  7 purchase totals = $954.15       $1,029.2001   $1,029.20   $1,029.15   $1,029.10