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 $249.74   5.163%   $262.6341   $262.63   $262.65   $262.60  
  Purchase #2 $69.39   11.250%   $77.1964   $77.20   $77.20   $77.20  
  Purchase #3 $218.30   9.291%   $238.5823   $238.58   $238.60   $238.60  
  Purchase #4 $130.41   3.585%   $135.0852   $135.09   $135.10   $135.10  
  Purchase #5 $87.64   4.565%   $91.6408   $91.64   $91.65   $91.60  
  Purchase #6 $161.39   5.382%   $170.076   $170.08   $170.10   $170.10  
  Purchase #7 $240.46   9.676%   $263.7269   $263.73   $263.75   $263.70  
  7 purchase totals = $1,157.33       $1,238.9417   $1,238.95   $1,239.05   $1,238.90