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 $192.54   5.261%   $202.6695   $202.67   $202.65   $202.70  
  Purchase #2 $19.46   9.147%   $21.24   $21.24   $21.25   $21.20  
  Purchase #3 $156.47   11.814%   $174.9554   $174.96   $174.95   $175.00  
  Purchase #4 $94.38   4.769%   $98.881   $98.88   $98.90   $98.90  
  Purchase #5 $43.72   3.646%   $45.314   $45.31   $45.30   $45.30  
  Purchase #6 $134.40   12.560%   $151.2806   $151.28   $151.30   $151.30  
  Purchase #7 $42.91   11.589%   $47.8828   $47.88   $47.90   $47.90  
  7 purchase totals = $683.88       $742.2233   $742.22   $742.25   $742.30