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 $207.72   11.744%   $232.1146   $232.11   $232.10   $232.10  
  Purchase #2 $56.57   7.627%   $60.8846   $60.88   $60.90   $60.90  
  Purchase #3 $192.83   13.233%   $218.3472   $218.35   $218.35   $218.30  
  Purchase #4 $227.71   11.753%   $254.4728   $254.47   $254.45   $254.50  
  Purchase #5 $153.39   11.847%   $171.5621   $171.56   $171.55   $171.60  
  Purchase #6 $247.70   9.186%   $270.4537   $270.45   $270.45   $270.50  
  Purchase #7 $186.78   11.789%   $208.7995   $208.80   $208.80   $208.80  
  7 purchase totals = $1,272.70       $1,416.6345   $1,416.62   $1,416.60   $1,416.70