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 $241.39   11.441%   $269.0074   $269.01   $269.00   $269.00  
  Purchase #2 $250.61   5.825%   $265.208   $265.21   $265.20   $265.20  
  Purchase #3 $54.99   10.814%   $60.9366   $60.94   $60.95   $60.90  
  Purchase #4 $181.47   12.136%   $203.4932   $203.49   $203.50   $203.50  
  Purchase #5 $183.32   4.253%   $191.1166   $191.12   $191.10   $191.10  
  Purchase #6 $220.48   11.630%   $246.1218   $246.12   $246.10   $246.10  
  Purchase #7 $31.49   5.803%   $33.3174   $33.32   $33.30   $33.30  
  7 purchase totals = $1,163.75       $1,269.2010   $1,269.21   $1,269.15   $1,269.10