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 $57.79   9.661%   $63.3731   $63.37   $63.35   $63.40  
  Purchase #2 $94.83   11.321%   $105.5657   $105.57   $105.55   $105.60  
  Purchase #3 $93.90   5.446%   $99.0138   $99.01   $99.00   $99.00  
  Purchase #4 $212.99   7.286%   $228.5085   $228.51   $228.50   $228.50  
  Purchase #5 $186.31   11.164%   $207.1096   $207.11   $207.10   $207.10  
  Purchase #6 $249.90   6.627%   $266.4609   $266.46   $266.45   $266.50  
  Purchase #7 $23.33   8.801%   $25.3833   $25.38   $25.40   $25.40  
  7 purchase totals = $919.05       $995.4149   $995.41   $995.35   $995.50