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 $212.41   11.473%   $236.7798   $236.78   $236.80   $236.80  
  Purchase #2 $31.44   6.225%   $33.3971   $33.40   $33.40   $33.40  
  Purchase #3 $206.67   12.628%   $232.7683   $232.77   $232.75   $232.80  
  Purchase #4 $166.69   8.681%   $181.1604   $181.16   $181.15   $181.20  
  Purchase #5 $71.81   10.169%   $79.1124   $79.11   $79.10   $79.10  
  Purchase #6 $243.39   10.686%   $269.3987   $269.40   $269.40   $269.40  
  Purchase #7 $204.71   11.416%   $228.0797   $228.08   $228.10   $228.10  
  7 purchase totals = $1,137.12       $1,260.6964   $1,260.70   $1,260.70   $1,260.80