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 $206.96   12.248%   $232.3085   $232.31   $232.30   $232.30  
  Purchase #2 $168.86   10.251%   $186.1698   $186.17   $186.15   $186.20  
  Purchase #3 $225.67   11.282%   $251.1301   $251.13   $251.15   $251.10  
  Purchase #4 $98.63   11.426%   $109.8995   $109.90   $109.90   $109.90  
  Purchase #5 $99.46   5.592%   $105.0218   $105.02   $105.00   $105.00  
  Purchase #6 $218.63   8.453%   $237.1108   $237.11   $237.10   $237.10  
  Purchase #7 $68.25   9.424%   $74.6819   $74.68   $74.70   $74.70  
  7 purchase totals = $1,086.46       $1,196.3224   $1,196.32   $1,196.30   $1,196.30