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 $162.32   10.143%   $178.7841   $178.78   $178.80   $178.80  
  Purchase #2 $223.97   3.568%   $231.9612   $231.96   $231.95   $232.00  
  Purchase #3 $21.39   4.196%   $22.2875   $22.29   $22.30   $22.30  
  Purchase #4 $226.83   6.264%   $241.0386   $241.04   $241.05   $241.00  
  Purchase #5 $140.72   11.144%   $156.4018   $156.40   $156.40   $156.40  
  Purchase #6 $193.80   7.742%   $208.804   $208.80   $208.80   $208.80  
  Purchase #7 $149.68   7.777%   $161.3206   $161.32   $161.30   $161.30  
  7 purchase totals = $1,118.71       $1,200.5978   $1,200.59   $1,200.60   $1,200.60