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 $218.78   13.559%   $248.4444   $248.44   $248.45   $248.40  
  Purchase #2 $110.76   9.566%   $121.3553   $121.36   $121.35   $121.40  
  Purchase #3 $53.52   4.702%   $56.0365   $56.04   $56.05   $56.00  
  Purchase #4 $230.73   6.308%   $245.2844   $245.28   $245.30   $245.30  
  Purchase #5 $219.64   5.201%   $231.0635   $231.06   $231.05   $231.10  
  Purchase #6 $51.69   9.239%   $56.4656   $56.47   $56.45   $56.50  
  Purchase #7 $77.47   12.370%   $87.053   $87.05   $87.05   $87.10  
  7 purchase totals = $962.59       $1,045.7027   $1,045.70   $1,045.70   $1,045.80