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 $162.84   4.142%   $169.5848   $169.58   $169.60   $169.60  
  Purchase #2 $224.77   12.178%   $252.1425   $252.14   $252.15   $252.10  
  Purchase #3 $79.71   10.416%   $88.0126   $88.01   $88.00   $88.00  
  Purchase #4 $217.90   13.346%   $246.9809   $246.98   $247.00   $247.00  
  Purchase #5 $132.92   12.117%   $149.0259   $149.03   $149.05   $149.00  
  Purchase #6 $143.79   7.593%   $154.708   $154.71   $154.70   $154.70  
  Purchase #7 $6.69   12.188%   $7.5054   $7.51   $7.50   $7.50  
  7 purchase totals = $968.62       $1,067.9601   $1,067.96   $1,068.00   $1,067.90