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 $246.45   8.762%   $268.0439   $268.04   $268.05   $268.00  
  Purchase #2 $115.55   5.466%   $121.866   $121.87   $121.85   $121.90  
  Purchase #3 $216.29   8.346%   $234.3416   $234.34   $234.35   $234.30  
  Purchase #4 $77.50   8.500%   $84.0875   $84.09   $84.10   $84.10  
  Purchase #5 $167.93   12.368%   $188.6996   $188.70   $188.70   $188.70  
  Purchase #6 $93.33   9.270%   $101.9817   $101.98   $102.00   $102.00  
  Purchase #7 $154.93   8.596%   $168.2478   $168.25   $168.25   $168.20  
  7 purchase totals = $1,071.98       $1,167.2681   $1,167.27   $1,167.30   $1,167.20