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 $63.57   5.281%   $66.9271   $66.93   $66.95   $66.90  
  Purchase #2 $184.36   7.305%   $197.8275   $197.83   $197.85   $197.80  
  Purchase #3 $134.51   9.629%   $147.462   $147.46   $147.45   $147.50  
  Purchase #4 $156.68   3.689%   $162.4599   $162.46   $162.45   $162.50  
  Purchase #5 $119.37   8.568%   $129.5976   $129.60   $129.60   $129.60  
  Purchase #6 $86.56   11.711%   $96.697   $96.70   $96.70   $96.70  
  Purchase #7 $213.27   12.557%   $240.0503   $240.05   $240.05   $240.10  
  7 purchase totals = $958.32       $1,041.0214   $1,041.03   $1,041.05   $1,041.10