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 $66.61   4.385%   $69.5308   $69.53   $69.55   $69.50  
  Purchase #2 $53.53   5.109%   $56.2648   $56.26   $56.25   $56.30  
  Purchase #3 $235.31   8.292%   $254.8219   $254.82   $254.80   $254.80  
  Purchase #4 $126.30   8.175%   $136.625   $136.63   $136.65   $136.60  
  Purchase #5 $6.84   5.707%   $7.2304   $7.23   $7.25   $7.20  
  Purchase #6 $153.95   7.621%   $165.6825   $165.68   $165.70   $165.70  
  Purchase #7 $30.67   13.418%   $34.7853   $34.79   $34.80   $34.80  
  7 purchase totals = $673.21       $724.9407   $724.94   $725.00   $724.90