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 $184.58   5.418%   $194.5805   $194.58   $194.60   $194.60  
  Purchase #2 $119.39   6.272%   $126.8781   $126.88   $126.90   $126.90  
  Purchase #3 $234.44   7.269%   $251.4814   $251.48   $251.50   $251.50  
  Purchase #4 $166.63   5.396%   $175.6214   $175.62   $175.60   $175.60  
  Purchase #5 $6.92   5.147%   $7.2762   $7.28   $7.30   $7.30  
  Purchase #6 $25.77   4.744%   $26.9925   $26.99   $27.00   $27.00  
  Purchase #7 $187.65   12.789%   $211.6486   $211.65   $211.65   $211.60  
  7 purchase totals = $925.38       $994.4787   $994.48   $994.55   $994.50