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 $178.61   3.551%   $184.9524   $184.95   $184.95   $185.00  
  Purchase #2 $174.70   10.821%   $193.6043   $193.60   $193.60   $193.60  
  Purchase #3 $23.57   4.837%   $24.7101   $24.71   $24.70   $24.70  
  Purchase #4 $240.45   5.133%   $252.7923   $252.79   $252.80   $252.80  
  Purchase #5 $135.86   9.708%   $149.0493   $149.05   $149.05   $149.00  
  Purchase #6 $236.45   7.537%   $254.2712   $254.27   $254.25   $254.30  
  Purchase #7 $71.61   8.225%   $77.4999   $77.50   $77.50   $77.50  
  7 purchase totals = $1,061.25       $1,136.8795   $1,136.87   $1,136.85   $1,136.90