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 $234.30   12.331%   $263.1915   $263.19   $263.20   $263.20  
  Purchase #2 $247.47   6.493%   $263.5382   $263.54   $263.55   $263.50  
  Purchase #3 $86.51   6.620%   $92.237   $92.24   $92.25   $92.20  
  Purchase #4 $160.65   11.411%   $178.9818   $178.98   $179.00   $179.00  
  Purchase #5 $83.83   13.772%   $95.3751   $95.38   $95.40   $95.40  
  Purchase #6 $118.98   12.584%   $133.9524   $133.95   $133.95   $134.00  
  Purchase #7 $156.38   9.784%   $171.6802   $171.68   $171.70   $171.70  
  7 purchase totals = $1,088.12       $1,198.9562   $1,198.96   $1,199.05   $1,199.00