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 $177.93   13.251%   $201.5075   $201.51   $201.50   $201.50  
  Purchase #2 $225.84   11.126%   $250.967   $250.97   $250.95   $251.00  
  Purchase #3 $160.66   4.265%   $167.5121   $167.51   $167.50   $167.50  
  Purchase #4 $210.43   12.403%   $236.5296   $236.53   $236.55   $236.50  
  Purchase #5 $176.33   7.566%   $189.6711   $189.67   $189.65   $189.70  
  Purchase #6 $220.30   8.698%   $239.4617   $239.46   $239.45   $239.50  
  Purchase #7 $97.91   12.195%   $109.8501   $109.85   $109.85   $109.90  
  7 purchase totals = $1,269.40       $1,395.4991   $1,395.50   $1,395.45   $1,395.60