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 $49.49   13.663%   $56.2518   $56.25   $56.25   $56.30  
  Purchase #2 $100.54   12.731%   $113.3397   $113.34   $113.35   $113.30  
  Purchase #3 $166.62   4.406%   $173.9613   $173.96   $173.95   $174.00  
  Purchase #4 $212.27   5.638%   $224.2378   $224.24   $224.25   $224.20  
  Purchase #5 $200.59   9.541%   $219.7283   $219.73   $219.75   $219.70  
  Purchase #6 $71.82   6.514%   $76.4984   $76.50   $76.50   $76.50  
  Purchase #7 $230.73   3.788%   $239.4701   $239.47   $239.45   $239.50  
  7 purchase totals = $1,032.06       $1,103.4874   $1,103.49   $1,103.50   $1,103.50