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 $61.27   12.605%   $68.9931   $68.99   $69.00   $69.00  
  Purchase #2 $232.87   11.845%   $260.4535   $260.45   $260.45   $260.50  
  Purchase #3 $202.27   13.777%   $230.1367   $230.14   $230.15   $230.10  
  Purchase #4 $102.68   3.716%   $106.4956   $106.50   $106.50   $106.50  
  Purchase #5 $149.48   11.324%   $166.4071   $166.41   $166.40   $166.40  
  Purchase #6 $206.79   12.698%   $233.0482   $233.05   $233.05   $233.00  
  Purchase #7 $127.57   13.118%   $144.3046   $144.30   $144.30   $144.30  
  7 purchase totals = $1,082.93       $1,209.8388   $1,209.84   $1,209.85   $1,209.80