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 $44.44   3.846%   $46.1492   $46.15   $46.15   $46.10  
  Purchase #2 $160.28   5.147%   $168.5296   $168.53   $168.55   $168.50  
  Purchase #3 $163.39   8.540%   $177.3435   $177.34   $177.35   $177.30  
  Purchase #4 $191.99   13.726%   $218.3425   $218.34   $218.35   $218.30  
  Purchase #5 $178.97   13.705%   $203.4978   $203.50   $203.50   $203.50  
  Purchase #6 $67.51   10.318%   $74.4757   $74.48   $74.50   $74.50  
  Purchase #7 $247.34   8.841%   $269.2073   $269.21   $269.20   $269.20  
  7 purchase totals = $1,053.92       $1,157.5456   $1,157.55   $1,157.60   $1,157.40