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 $51.91   9.833%   $57.0143   $57.01   $57.00   $57.00  
  Purchase #2 $43.96   8.342%   $47.6271   $47.63   $47.65   $47.60  
  Purchase #3 $240.59   10.143%   $264.993   $264.99   $265.00   $265.00  
  Purchase #4 $71.61   4.675%   $74.9578   $74.96   $74.95   $75.00  
  Purchase #5 $241.93   11.648%   $270.11   $270.11   $270.10   $270.10  
  Purchase #6 $88.99   8.144%   $96.2373   $96.24   $96.25   $96.20  
  Purchase #7 $134.46   3.678%   $139.4054   $139.41   $139.40   $139.40  
  7 purchase totals = $873.45       $950.3449   $950.35   $950.35   $950.30