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 $76.75   10.356%   $84.6982   $84.70   $84.70   $84.70  
  Purchase #2 $231.38   12.774%   $260.9365   $260.94   $260.95   $260.90  
  Purchase #3 $222.88   5.261%   $234.6057   $234.61   $234.60   $234.60  
  Purchase #4 $82.49   3.648%   $85.4992   $85.50   $85.50   $85.50  
  Purchase #5 $102.49   10.266%   $113.0116   $113.01   $113.00   $113.00  
  Purchase #6 $66.26   10.670%   $73.3299   $73.33   $73.35   $73.30  
  Purchase #7 $226.69   4.250%   $236.3243   $236.32   $236.30   $236.30  
  7 purchase totals = $1,008.94       $1,088.4054   $1,088.41   $1,088.40   $1,088.30