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 $184.39   13.724%   $209.6957   $209.70   $209.70   $209.70  
  Purchase #2 $228.40   4.803%   $239.3701   $239.37   $239.35   $239.40  
  Purchase #3 $151.98   6.536%   $161.9134   $161.91   $161.90   $161.90  
  Purchase #4 $74.96   11.691%   $83.7236   $83.72   $83.70   $83.70  
  Purchase #5 $10.29   4.448%   $10.7477   $10.75   $10.75   $10.70  
  Purchase #6 $96.71   9.259%   $105.6644   $105.66   $105.65   $105.70  
  Purchase #7 $195.85   4.120%   $203.919   $203.92   $203.90   $203.90  
  7 purchase totals = $942.58       $1,015.0339   $1,015.03   $1,014.95   $1,015.00