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 $198.80   6.537%   $211.7956   $211.80   $211.80   $211.80  
  Purchase #2 $179.87   6.727%   $191.9699   $191.97   $191.95   $192.00  
  Purchase #3 $77.99   6.479%   $83.043   $83.04   $83.05   $83.00  
  Purchase #4 $19.52   7.310%   $20.9469   $20.95   $20.95   $20.90  
  Purchase #5 $221.48   5.365%   $233.3624   $233.36   $233.35   $233.40  
  Purchase #6 $54.30   4.185%   $56.5725   $56.57   $56.55   $56.60  
  Purchase #7 $144.38   13.483%   $163.8468   $163.85   $163.85   $163.80  
  7 purchase totals = $896.34       $961.5371   $961.54   $961.50   $961.50