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 $64.93   6.149%   $68.9225   $68.92   $68.90   $68.90  
  Purchase #2 $205.53   8.502%   $223.0042   $223.00   $223.00   $223.00  
  Purchase #3 $221.83   7.333%   $238.0968   $238.10   $238.10   $238.10  
  Purchase #4 $247.67   12.230%   $277.96   $277.96   $277.95   $278.00  
  Purchase #5 $49.30   8.538%   $53.5092   $53.51   $53.50   $53.50  
  Purchase #6 $84.41   11.135%   $93.8091   $93.81   $93.80   $93.80  
  Purchase #7 $242.40   10.559%   $267.995   $268.00   $268.00   $268.00  
  7 purchase totals = $1,116.07       $1,223.2968   $1,223.30   $1,223.25   $1,223.30