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 $151.35   6.323%   $160.9199   $160.92   $160.90   $160.90  
  Purchase #2 $191.81   6.353%   $203.9957   $204.00   $204.00   $204.00  
  Purchase #3 $186.26   12.579%   $209.6896   $209.69   $209.70   $209.70  
  Purchase #4 $72.76   6.250%   $77.3075   $77.31   $77.30   $77.30  
  Purchase #5 $120.89   12.515%   $136.0194   $136.02   $136.00   $136.00  
  Purchase #6 $67.68   6.705%   $72.2179   $72.22   $72.20   $72.20  
  Purchase #7 $127.62   7.507%   $137.2004   $137.20   $137.20   $137.20  
  7 purchase totals = $918.37       $997.3504   $997.36   $997.30   $997.30