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 $202.38   13.240%   $229.1751   $229.18   $229.20   $229.20  
  Purchase #2 $155.52   9.207%   $169.8387   $169.84   $169.85   $169.80  
  Purchase #3 $130.48   9.486%   $142.8573   $142.86   $142.85   $142.90  
  Purchase #4 $68.94   3.493%   $71.3481   $71.35   $71.35   $71.30  
  Purchase #5 $114.34   9.190%   $124.8478   $124.85   $124.85   $124.80  
  Purchase #6 $211.54   13.231%   $239.5289   $239.53   $239.55   $239.50  
  Purchase #7 $76.33   9.163%   $83.3241   $83.32   $83.30   $83.30  
  7 purchase totals = $959.53       $1,060.9200   $1,060.93   $1,060.95   $1,060.80