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 $193.55   13.140%   $218.9825   $218.98   $219.00   $219.00  
  Purchase #2 $169.69   10.195%   $186.9899   $186.99   $187.00   $187.00  
  Purchase #3 $21.67   6.488%   $23.0759   $23.08   $23.10   $23.10  
  Purchase #4 $77.32   5.838%   $81.8339   $81.83   $81.85   $81.80  
  Purchase #5 $89.35   4.373%   $93.2573   $93.26   $93.25   $93.30  
  Purchase #6 $173.69   5.512%   $183.2638   $183.26   $183.25   $183.30  
  Purchase #7 $201.70   12.740%   $227.3966   $227.40   $227.40   $227.40  
  7 purchase totals = $926.97       $1,014.7999   $1,014.80   $1,014.85   $1,014.90