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 $242.82   13.690%   $276.0621   $276.06   $276.05   $276.10  
  Purchase #2 $65.95   4.139%   $68.6797   $68.68   $68.70   $68.70  
  Purchase #3 $114.33   11.760%   $127.7752   $127.78   $127.80   $127.80  
  Purchase #4 $166.75   4.602%   $174.4238   $174.42   $174.40   $174.40  
  Purchase #5 $114.46   3.278%   $118.212   $118.21   $118.20   $118.20  
  Purchase #6 $95.35   5.626%   $100.7144   $100.71   $100.70   $100.70  
  Purchase #7 $119.46   12.840%   $134.7987   $134.80   $134.80   $134.80  
  7 purchase totals = $919.12       $1,000.6659   $1,000.66   $1,000.65   $1,000.70