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 $224.66   11.861%   $251.3069   $251.31   $251.30   $251.30  
  Purchase #2 $36.65   12.799%   $41.3408   $41.34   $41.35   $41.30  
  Purchase #3 $203.83   12.488%   $229.2843   $229.28   $229.30   $229.30  
  Purchase #4 $86.62   9.784%   $95.0949   $95.09   $95.10   $95.10  
  Purchase #5 $16.35   8.275%   $17.703   $17.70   $17.70   $17.70  
  Purchase #6 $168.84   3.237%   $174.3054   $174.31   $174.30   $174.30  
  Purchase #7 $68.76   7.213%   $73.7197   $73.72   $73.70   $73.70  
  7 purchase totals = $805.71       $882.7550   $882.75   $882.75   $882.70