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 $232.39   11.481%   $259.0707   $259.07   $259.05   $259.10  
  Purchase #2 $241.26   5.503%   $254.5365   $254.54   $254.55   $254.50  
  Purchase #3 $32.96   3.369%   $34.0704   $34.07   $34.05   $34.10  
  Purchase #4 $140.92   7.806%   $151.9202   $151.92   $151.90   $151.90  
  Purchase #5 $50.85   10.377%   $56.1267   $56.13   $56.15   $56.10  
  Purchase #6 $243.87   6.463%   $259.6313   $259.63   $259.65   $259.60  
  Purchase #7 $73.25   5.150%   $77.0224   $77.02   $77.00   $77.00  
  7 purchase totals = $1,015.50       $1,092.3782   $1,092.38   $1,092.35   $1,092.30