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 $158.98   9.438%   $173.9845   $173.98   $174.00   $174.00  
  Purchase #2 $83.91   13.497%   $95.2353   $95.24   $95.25   $95.20  
  Purchase #3 $103.94   3.629%   $107.712   $107.71   $107.70   $107.70  
  Purchase #4 $222.44   5.166%   $233.9313   $233.93   $233.95   $233.90  
  Purchase #5 $186.88   13.236%   $211.6154   $211.62   $211.60   $211.60  
  Purchase #6 $5.46   11.201%   $6.0716   $6.07   $6.05   $6.10  
  Purchase #7 $182.70   4.410%   $190.7571   $190.76   $190.75   $190.80  
  7 purchase totals = $944.31       $1,019.3072   $1,019.31   $1,019.30   $1,019.30