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 $109.75   12.684%   $123.6707   $123.67   $123.65   $123.70  
  Purchase #2 $96.66   3.697%   $100.2335   $100.23   $100.25   $100.20  
  Purchase #3 $184.28   4.703%   $192.9467   $192.95   $192.95   $192.90  
  Purchase #4 $250.71   3.269%   $258.9057   $258.91   $258.90   $258.90  
  Purchase #5 $247.71   9.132%   $270.3309   $270.33   $270.35   $270.30  
  Purchase #6 $147.52   12.198%   $165.5145   $165.51   $165.50   $165.50  
  Purchase #7 $60.36   12.702%   $68.0269   $68.03   $68.05   $68.00  
  7 purchase totals = $1,096.99       $1,179.6289   $1,179.63   $1,179.65   $1,179.50