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 $210.90   12.281%   $236.8006   $236.80   $236.80   $236.80  
  Purchase #2 $231.87   3.709%   $240.4701   $240.47   $240.45   $240.50  
  Purchase #3 $109.76   3.569%   $113.6773   $113.68   $113.70   $113.70  
  Purchase #4 $59.95   9.207%   $65.4696   $65.47   $65.45   $65.50  
  Purchase #5 $172.97   7.526%   $185.9877   $185.99   $186.00   $186.00  
  Purchase #6 $58.80   8.692%   $63.9109   $63.91   $63.90   $63.90  
  Purchase #7 $148.96   3.390%   $154.0097   $154.01   $154.00   $154.00  
  7 purchase totals = $993.21       $1,060.3259   $1,060.33   $1,060.30   $1,060.40