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 $91.84   5.241%   $96.6533   $96.65   $96.65   $96.70  
  Purchase #2 $50.84   10.609%   $56.2336   $56.23   $56.25   $56.20  
  Purchase #3 $225.63   12.182%   $253.1162   $253.12   $253.10   $253.10  
  Purchase #4 $141.55   4.299%   $147.6352   $147.64   $147.65   $147.60  
  Purchase #5 $207.90   8.205%   $224.9582   $224.96   $224.95   $225.00  
  Purchase #6 $41.57   11.688%   $46.4287   $46.43   $46.45   $46.40  
  Purchase #7 $215.49   11.461%   $240.1873   $240.19   $240.20   $240.20  
  7 purchase totals = $974.82       $1,065.2125   $1,065.22   $1,065.25   $1,065.20