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 $154.64   5.159%   $162.6179   $162.62   $162.60   $162.60  
  Purchase #2 $83.33   7.574%   $89.6414   $89.64   $89.65   $89.60  
  Purchase #3 $207.59   13.201%   $234.994   $234.99   $235.00   $235.00  
  Purchase #4 $88.75   12.196%   $99.574   $99.57   $99.55   $99.60  
  Purchase #5 $216.46   10.304%   $238.764   $238.76   $238.75   $238.80  
  Purchase #6 $23.25   13.283%   $26.3383   $26.34   $26.35   $26.30  
  Purchase #7 $240.36   13.543%   $272.912   $272.91   $272.90   $272.90  
  7 purchase totals = $1,014.38       $1,124.8416   $1,124.83   $1,124.80   $1,124.80