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 $201.51   3.847%   $209.2621   $209.26   $209.25   $209.30  
  Purchase #2 $177.57   11.446%   $197.8947   $197.89   $197.90   $197.90  
  Purchase #3 $31.29   4.318%   $32.6411   $32.64   $32.65   $32.60  
  Purchase #4 $235.91   3.301%   $243.6974   $243.70   $243.70   $243.70  
  Purchase #5 $176.45   9.368%   $192.9798   $192.98   $193.00   $193.00  
  Purchase #6 $51.66   4.687%   $54.0813   $54.08   $54.10   $54.10  
  Purchase #7 $157.27   9.791%   $172.6683   $172.67   $172.65   $172.70  
  7 purchase totals = $1,031.66       $1,103.2247   $1,103.22   $1,103.25   $1,103.30