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 $173.60   6.155%   $184.2851   $184.29   $184.30   $184.30  
  Purchase #2 $233.29   10.395%   $257.5405   $257.54   $257.55   $257.50  
  Purchase #3 $194.68   9.772%   $213.7041   $213.70   $213.70   $213.70  
  Purchase #4 $245.87   12.285%   $276.0751   $276.08   $276.10   $276.10  
  Purchase #5 $131.71   11.766%   $147.207   $147.21   $147.20   $147.20  
  Purchase #6 $47.37   10.183%   $52.1937   $52.19   $52.20   $52.20  
  Purchase #7 $206.68   4.280%   $215.5259   $215.53   $215.55   $215.50  
  7 purchase totals = $1,233.20       $1,346.5314   $1,346.54   $1,346.60   $1,346.50