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 $162.72   12.461%   $182.9965   $183.00   $183.00   $183.00  
  Purchase #2 $31.27   6.537%   $33.3141   $33.31   $33.30   $33.30  
  Purchase #3 $80.36   5.768%   $84.9952   $85.00   $85.00   $85.00  
  Purchase #4 $229.26   5.848%   $242.6671   $242.67   $242.65   $242.70  
  Purchase #5 $121.71   4.663%   $127.3853   $127.39   $127.40   $127.40  
  Purchase #6 $223.45   12.107%   $250.5031   $250.50   $250.50   $250.50  
  Purchase #7 $208.64   8.464%   $226.2993   $226.30   $226.30   $226.30  
  7 purchase totals = $1,057.41       $1,148.1606   $1,148.17   $1,148.15   $1,148.20