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 $113.72   5.163%   $119.5914   $119.59   $119.60   $119.60  
  Purchase #2 $246.83   12.598%   $277.9256   $277.93   $277.95   $277.90  
  Purchase #3 $199.96   10.458%   $220.8718   $220.87   $220.85   $220.90  
  Purchase #4 $65.79   12.176%   $73.8006   $73.80   $73.80   $73.80  
  Purchase #5 $236.50   8.608%   $256.8579   $256.86   $256.85   $256.90  
  Purchase #6 $207.31   10.177%   $228.4079   $228.41   $228.40   $228.40  
  Purchase #7 $7.84   8.607%   $8.5148   $8.51   $8.50   $8.50  
  7 purchase totals = $1,077.95       $1,185.9700   $1,185.97   $1,185.95   $1,186.00