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 $203.64   7.591%   $219.0983   $219.10   $219.10   $219.10  
  Purchase #2 $70.94   3.341%   $73.3101   $73.31   $73.30   $73.30  
  Purchase #3 $78.87   4.129%   $82.1265   $82.13   $82.15   $82.10  
  Purchase #4 $76.35   6.515%   $81.3242   $81.32   $81.30   $81.30  
  Purchase #5 $179.45   7.343%   $192.627   $192.63   $192.65   $192.60  
  Purchase #6 $122.29   3.488%   $126.5555   $126.56   $126.55   $126.60  
  Purchase #7 $63.90   10.585%   $70.6638   $70.66   $70.65   $70.70  
  7 purchase totals = $795.44       $845.7054   $845.71   $845.70   $845.70