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 $182.33   8.120%   $197.1352   $197.14   $197.15   $197.10  
  Purchase #2 $110.96   6.634%   $118.3211   $118.32   $118.30   $118.30  
  Purchase #3 $226.27   3.285%   $233.703   $233.70   $233.70   $233.70  
  Purchase #4 $240.28   11.553%   $268.0395   $268.04   $268.05   $268.00  
  Purchase #5 $5.85   11.314%   $6.5119   $6.51   $6.50   $6.50  
  Purchase #6 $247.92   6.273%   $263.472   $263.47   $263.45   $263.50  
  Purchase #7 $64.67   7.120%   $69.2745   $69.27   $69.25   $69.30  
  7 purchase totals = $1,078.28       $1,156.4572   $1,156.45   $1,156.40   $1,156.40