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 $73.57   3.231%   $75.947   $75.95   $75.95   $75.90  
  Purchase #2 $152.94   7.135%   $163.8523   $163.85   $163.85   $163.90  
  Purchase #3 $47.39   10.541%   $52.3854   $52.39   $52.40   $52.40  
  Purchase #4 $212.37   13.250%   $240.509   $240.51   $240.50   $240.50  
  Purchase #5 $16.96   6.678%   $18.0926   $18.09   $18.10   $18.10  
  Purchase #6 $222.93   13.485%   $252.9921   $252.99   $253.00   $253.00  
  Purchase #7 $39.43   11.435%   $43.9388   $43.94   $43.95   $43.90  
  7 purchase totals = $765.59       $847.7172   $847.72   $847.75   $847.70