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 $68.93   10.377%   $76.0829   $76.08   $76.10   $76.10  
  Purchase #2 $184.89   10.138%   $203.6341   $203.63   $203.65   $203.60  
  Purchase #3 $90.53   7.232%   $97.0771   $97.08   $97.10   $97.10  
  Purchase #4 $201.88   7.773%   $217.5721   $217.57   $217.55   $217.60  
  Purchase #5 $94.91   12.570%   $106.8402   $106.84   $106.85   $106.80  
  Purchase #6 $12.50   12.798%   $14.0998   $14.10   $14.10   $14.10  
  Purchase #7 $70.98   7.137%   $76.0458   $76.05   $76.05   $76.00  
  7 purchase totals = $724.62       $791.3520   $791.35   $791.40   $791.30