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 $220.93   12.483%   $248.5087   $248.51   $248.50   $248.50  
  Purchase #2 $173.66   4.199%   $180.952   $180.95   $180.95   $181.00  
  Purchase #3 $61.27   5.234%   $64.4769   $64.48   $64.50   $64.50  
  Purchase #4 $181.48   8.449%   $196.8132   $196.81   $196.80   $196.80  
  Purchase #5 $23.99   5.731%   $25.3649   $25.36   $25.35   $25.40  
  Purchase #6 $114.65   9.783%   $125.8662   $125.87   $125.85   $125.90  
  Purchase #7 $211.84   8.113%   $229.0266   $229.03   $229.05   $229.00  
  7 purchase totals = $987.82       $1,071.0085   $1,071.01   $1,071.00   $1,071.10