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 $232.62   9.518%   $254.7608   $254.76   $254.75   $254.80  
  Purchase #2 $148.77   7.488%   $159.9099   $159.91   $159.90   $159.90  
  Purchase #3 $176.51   13.823%   $200.909   $200.91   $200.90   $200.90  
  Purchase #4 $161.45   3.442%   $167.0071   $167.01   $167.00   $167.00  
  Purchase #5 $8.92   9.524%   $9.7695   $9.77   $9.75   $9.80  
  Purchase #6 $146.75   11.384%   $163.456   $163.46   $163.45   $163.50  
  Purchase #7 $232.62   5.182%   $244.6744   $244.67   $244.65   $244.70  
  7 purchase totals = $1,107.64       $1,200.4867   $1,200.49   $1,200.40   $1,200.60