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 $211.52   9.236%   $231.056   $231.06   $231.05   $231.10  
  Purchase #2 $102.94   9.469%   $112.6874   $112.69   $112.70   $112.70  
  Purchase #3 $179.31   6.723%   $191.365   $191.37   $191.35   $191.40  
  Purchase #4 $119.52   12.745%   $134.7528   $134.75   $134.75   $134.80  
  Purchase #5 $210.30   5.771%   $222.4364   $222.44   $222.45   $222.40  
  Purchase #6 $216.63   3.465%   $224.1362   $224.14   $224.15   $224.10  
  Purchase #7 $174.97   13.291%   $198.2253   $198.23   $198.25   $198.20  
  7 purchase totals = $1,215.19       $1,314.6591   $1,314.68   $1,314.70   $1,314.70