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 $174.35   3.313%   $180.1262   $180.13   $180.15   $180.10  
  Purchase #2 $116.72   8.518%   $126.6622   $126.66   $126.65   $126.70  
  Purchase #3 $102.77   8.109%   $111.1036   $111.10   $111.10   $111.10  
  Purchase #4 $102.62   6.169%   $108.9506   $108.95   $108.95   $109.00  
  Purchase #5 $190.76   10.622%   $211.0225   $211.02   $211.00   $211.00  
  Purchase #6 $157.62   10.648%   $174.4034   $174.40   $174.40   $174.40  
  Purchase #7 $235.94   5.775%   $249.5655   $249.57   $249.55   $249.60  
  7 purchase totals = $1,080.78       $1,161.8340   $1,161.83   $1,161.80   $1,161.90