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 $65.87   8.127%   $71.2233   $71.22   $71.20   $71.20  
  Purchase #2 $107.34   7.721%   $115.6277   $115.63   $115.65   $115.60  
  Purchase #3 $173.65   5.387%   $183.0045   $183.00   $183.00   $183.00  
  Purchase #4 $216.80   6.313%   $230.4866   $230.49   $230.50   $230.50  
  Purchase #5 $221.74   3.315%   $229.0907   $229.09   $229.10   $229.10  
  Purchase #6 $31.44   3.456%   $32.5266   $32.53   $32.55   $32.50  
  Purchase #7 $171.28   5.839%   $181.281   $181.28   $181.30   $181.30  
  7 purchase totals = $988.12       $1,043.2404   $1,043.24   $1,043.30   $1,043.20