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 $206.32   13.274%   $233.7069   $233.71   $233.70   $233.70  
  Purchase #2 $228.85   9.460%   $250.4992   $250.50   $250.50   $250.50  
  Purchase #3 $116.56   12.350%   $130.9552   $130.96   $130.95   $131.00  
  Purchase #4 $64.38   11.452%   $71.7528   $71.75   $71.75   $71.80  
  Purchase #5 $247.46   8.661%   $268.8925   $268.89   $268.90   $268.90  
  Purchase #6 $55.81   13.577%   $63.3873   $63.39   $63.40   $63.40  
  Purchase #7 $219.48   3.331%   $226.7909   $226.79   $226.80   $226.80  
  7 purchase totals = $1,138.86       $1,245.9848   $1,245.99   $1,246.00   $1,246.10