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 $200.27   13.763%   $227.8332   $227.83   $227.85   $227.80  
  Purchase #2 $245.66   9.485%   $268.9609   $268.96   $268.95   $269.00  
  Purchase #3 $183.95   7.564%   $197.864   $197.86   $197.85   $197.90  
  Purchase #4 $164.25   4.714%   $171.9927   $171.99   $172.00   $172.00  
  Purchase #5 $13.86   11.751%   $15.4887   $15.49   $15.50   $15.50  
  Purchase #6 $43.92   4.743%   $46.0031   $46.00   $46.00   $46.00  
  Purchase #7 $136.35   9.396%   $149.1614   $149.16   $149.15   $149.20  
  7 purchase totals = $988.26       $1,077.3040   $1,077.29   $1,077.30   $1,077.40