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 $59.31   6.266%   $63.0264   $63.03   $63.05   $63.00  
  Purchase #2 $216.48   7.103%   $231.8566   $231.86   $231.85   $231.90  
  Purchase #3 $157.92   10.463%   $174.4432   $174.44   $174.45   $174.40  
  Purchase #4 $39.27   6.773%   $41.9298   $41.93   $41.95   $41.90  
  Purchase #5 $177.84   8.633%   $193.1929   $193.19   $193.20   $193.20  
  Purchase #6 $120.63   10.507%   $133.3046   $133.30   $133.30   $133.30  
  Purchase #7 $157.77   13.499%   $179.0674   $179.07   $179.05   $179.10  
  7 purchase totals = $929.22       $1,016.8209   $1,016.82   $1,016.85   $1,016.80