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 $203.98   13.771%   $232.0701   $232.07   $232.05   $232.10  
  Purchase #2 $167.45   8.227%   $181.2261   $181.23   $181.25   $181.20  
  Purchase #3 $30.59   8.765%   $33.2712   $33.27   $33.25   $33.30  
  Purchase #4 $165.62   12.408%   $186.1701   $186.17   $186.15   $186.20  
  Purchase #5 $178.66   7.248%   $191.6093   $191.61   $191.60   $191.60  
  Purchase #6 $175.72   4.597%   $183.7978   $183.80   $183.80   $183.80  
  Purchase #7 $18.55   6.843%   $19.8194   $19.82   $19.80   $19.80  
  7 purchase totals = $940.57       $1,027.9640   $1,027.97   $1,027.90   $1,028.00