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 $247.34   11.194%   $275.0272   $275.03   $275.05   $275.00  
  Purchase #2 $188.93   12.473%   $212.4952   $212.50   $212.50   $212.50  
  Purchase #3 $67.97   7.512%   $73.0759   $73.08   $73.10   $73.10  
  Purchase #4 $119.58   6.855%   $127.7772   $127.78   $127.80   $127.80  
  Purchase #5 $102.63   9.102%   $111.9714   $111.97   $111.95   $112.00  
  Purchase #6 $168.34   9.333%   $184.0512   $184.05   $184.05   $184.10  
  Purchase #7 $59.97   8.779%   $65.2348   $65.23   $65.25   $65.20  
  7 purchase totals = $954.76       $1,049.6329   $1,049.64   $1,049.70   $1,049.70