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 $248.65   6.153%   $263.9494   $263.95   $263.95   $263.90  
  Purchase #2 $136.44   7.873%   $147.1819   $147.18   $147.20   $147.20  
  Purchase #3 $219.37   6.679%   $234.0217   $234.02   $234.00   $234.00  
  Purchase #4 $222.41   5.768%   $235.2386   $235.24   $235.25   $235.20  
  Purchase #5 $224.82   12.502%   $252.927   $252.93   $252.95   $252.90  
  Purchase #6 $200.49   7.826%   $216.1803   $216.18   $216.20   $216.20  
  Purchase #7 $27.74   7.341%   $29.7764   $29.78   $29.80   $29.80  
  7 purchase totals = $1,279.92       $1,379.2753   $1,379.28   $1,379.35   $1,379.20