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 $179.92   13.351%   $203.9411   $203.94   $203.95   $203.90  
  Purchase #2 $164.77   11.262%   $183.3264   $183.33   $183.35   $183.30  
  Purchase #3 $127.67   12.593%   $143.7475   $143.75   $143.75   $143.70  
  Purchase #4 $113.72   4.861%   $119.2479   $119.25   $119.25   $119.20  
  Purchase #5 $219.95   6.847%   $235.01   $235.01   $235.00   $235.00  
  Purchase #6 $143.83   3.121%   $148.3189   $148.32   $148.30   $148.30  
  Purchase #7 $24.69   10.135%   $27.1923   $27.19   $27.20   $27.20  
  7 purchase totals = $974.55       $1,060.7841   $1,060.79   $1,060.80   $1,060.60