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 $67.83   7.144%   $72.6758   $72.68   $72.70   $72.70  
  Purchase #2 $41.37   11.531%   $46.1404   $46.14   $46.15   $46.10  
  Purchase #3 $67.91   7.714%   $73.1486   $73.15   $73.15   $73.10  
  Purchase #4 $80.84   9.804%   $88.7656   $88.77   $88.75   $88.80  
  Purchase #5 $133.31   13.795%   $151.7001   $151.70   $151.70   $151.70  
  Purchase #6 $62.81   10.712%   $69.5382   $69.54   $69.55   $69.50  
  Purchase #7 $230.79   7.158%   $247.3099   $247.31   $247.30   $247.30  
  7 purchase totals = $684.86       $749.2786   $749.29   $749.30   $749.20