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 $87.52   9.444%   $95.7854   $95.79   $95.80   $95.80  
  Purchase #2 $42.65   13.721%   $48.502   $48.50   $48.50   $48.50  
  Purchase #3 $106.95   12.620%   $120.4471   $120.45   $120.45   $120.40  
  Purchase #4 $58.75   8.766%   $63.9   $63.90   $63.90   $63.90  
  Purchase #5 $176.43   9.362%   $192.9474   $192.95   $192.95   $192.90  
  Purchase #6 $90.75   6.644%   $96.7794   $96.78   $96.80   $96.80  
  Purchase #7 $168.99   10.466%   $186.6765   $186.68   $186.70   $186.70  
  7 purchase totals = $732.04       $805.0378   $805.05   $805.10   $805.00