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 $10.88   3.690%   $11.2815   $11.28   $11.30   $11.30  
  Purchase #2 $246.43   9.419%   $269.6412   $269.64   $269.65   $269.60  
  Purchase #3 $208.49   12.302%   $234.1384   $234.14   $234.15   $234.10  
  Purchase #4 $22.99   4.836%   $24.1018   $24.10   $24.10   $24.10  
  Purchase #5 $103.54   7.201%   $110.9959   $111.00   $111.00   $111.00  
  Purchase #6 $248.60   13.555%   $282.2977   $282.30   $282.30   $282.30  
  Purchase #7 $123.75   11.757%   $138.2993   $138.30   $138.30   $138.30  
  7 purchase totals = $964.68       $1,070.7558   $1,070.76   $1,070.80   $1,070.70