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 $53.42   9.544%   $58.5184   $58.52   $58.50   $58.50  
  Purchase #2 $233.91   5.473%   $246.7119   $246.71   $246.70   $246.70  
  Purchase #3 $211.96   6.630%   $226.0129   $226.01   $226.00   $226.00  
  Purchase #4 $221.94   6.796%   $237.023   $237.02   $237.00   $237.00  
  Purchase #5 $52.52   13.532%   $59.627   $59.63   $59.65   $59.60  
  Purchase #6 $24.99   3.495%   $25.8634   $25.86   $25.85   $25.90  
  Purchase #7 $55.67   13.440%   $63.152   $63.15   $63.15   $63.20  
  7 purchase totals = $854.41       $916.9086   $916.90   $916.85   $916.90