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 $235.75   5.162%   $247.9194   $247.92   $247.90   $247.90  
  Purchase #2 $101.98   11.621%   $113.8311   $113.83   $113.85   $113.80  
  Purchase #3 $13.92   4.597%   $14.5599   $14.56   $14.55   $14.60  
  Purchase #4 $144.98   4.711%   $151.81   $151.81   $151.80   $151.80  
  Purchase #5 $39.54   4.702%   $41.3992   $41.40   $41.40   $41.40  
  Purchase #6 $180.26   7.242%   $193.3144   $193.31   $193.30   $193.30  
  Purchase #7 $75.43   11.849%   $84.3677   $84.37   $84.35   $84.40  
  7 purchase totals = $791.86       $847.2017   $847.20   $847.15   $847.20