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 $126.46   11.660%   $141.2052   $141.21   $141.20   $141.20  
  Purchase #2 $242.39   8.612%   $263.2646   $263.26   $263.25   $263.30  
  Purchase #3 $165.38   3.448%   $171.0823   $171.08   $171.10   $171.10  
  Purchase #4 $223.61   9.375%   $244.5734   $244.57   $244.55   $244.60  
  Purchase #5 $202.40   8.642%   $219.8914   $219.89   $219.90   $219.90  
  Purchase #6 $38.67   8.614%   $42.001   $42.00   $42.00   $42.00  
  Purchase #7 $163.48   9.462%   $178.9485   $178.95   $178.95   $178.90  
  7 purchase totals = $1,162.39       $1,260.9664   $1,260.96   $1,260.95   $1,261.00