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 $192.35   9.851%   $211.2984   $211.30   $211.30   $211.30  
  Purchase #2 $156.44   10.350%   $172.6315   $172.63   $172.65   $172.60  
  Purchase #3 $118.75   6.220%   $126.1363   $126.14   $126.15   $126.10  
  Purchase #4 $246.81   9.272%   $269.6942   $269.69   $269.70   $269.70  
  Purchase #5 $177.90   13.779%   $202.4128   $202.41   $202.40   $202.40  
  Purchase #6 $198.73   12.406%   $223.3844   $223.38   $223.40   $223.40  
  Purchase #7 $24.81   13.332%   $28.1177   $28.12   $28.10   $28.10  
  7 purchase totals = $1,115.79       $1,233.6753   $1,233.67   $1,233.70   $1,233.60