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 $206.25   11.641%   $230.2596   $230.26   $230.25   $230.30  
  Purchase #2 $93.46   5.772%   $98.8545   $98.85   $98.85   $98.90  
  Purchase #3 $140.59   13.384%   $159.4066   $159.41   $159.40   $159.40  
  Purchase #4 $149.55   11.300%   $166.4492   $166.45   $166.45   $166.40  
  Purchase #5 $55.55   11.678%   $62.0371   $62.04   $62.05   $62.00  
  Purchase #6 $233.94   13.341%   $265.1499   $265.15   $265.15   $265.10  
  Purchase #7 $181.86   5.599%   $192.0423   $192.04   $192.05   $192.00  
  7 purchase totals = $1,061.20       $1,174.1992   $1,174.20   $1,174.20   $1,174.10