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 $212.52   10.241%   $234.2842   $234.28   $234.30   $234.30  
  Purchase #2 $86.79   10.569%   $95.9628   $95.96   $95.95   $96.00  
  Purchase #3 $209.51   4.276%   $218.4686   $218.47   $218.45   $218.50  
  Purchase #4 $150.63   4.861%   $157.9521   $157.95   $157.95   $158.00  
  Purchase #5 $183.30   8.629%   $199.117   $199.12   $199.10   $199.10  
  Purchase #6 $40.54   10.828%   $44.9297   $44.93   $44.95   $44.90  
  Purchase #7 $119.74   6.727%   $127.7949   $127.79   $127.80   $127.80  
  7 purchase totals = $1,003.03       $1,078.5093   $1,078.50   $1,078.50   $1,078.60