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 $23.67   5.509%   $24.974   $24.97   $24.95   $25.00  
  Purchase #2 $82.64   11.229%   $91.9196   $91.92   $91.90   $91.90  
  Purchase #3 $113.79   11.808%   $127.2263   $127.23   $127.25   $127.20  
  Purchase #4 $87.58   9.350%   $95.7687   $95.77   $95.75   $95.80  
  Purchase #5 $182.98   8.539%   $198.6047   $198.60   $198.60   $198.60  
  Purchase #6 $138.70   5.169%   $145.8694   $145.87   $145.85   $145.90  
  Purchase #7 $117.47   5.804%   $124.288   $124.29   $124.30   $124.30  
  7 purchase totals = $746.83       $808.6507   $808.65   $808.60   $808.70