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 $110.47   13.672%   $125.5735   $125.57   $125.55   $125.60  
  Purchase #2 $114.54   3.108%   $118.0999   $118.10   $118.10   $118.10  
  Purchase #3 $250.83   10.372%   $276.8461   $276.85   $276.85   $276.80  
  Purchase #4 $134.26   9.659%   $147.2282   $147.23   $147.25   $147.20  
  Purchase #5 $61.37   12.348%   $68.948   $68.95   $68.95   $68.90  
  Purchase #6 $172.86   8.343%   $187.2817   $187.28   $187.30   $187.30  
  Purchase #7 $145.84   10.140%   $160.6282   $160.63   $160.65   $160.60  
  7 purchase totals = $990.17       $1,084.6056   $1,084.61   $1,084.65   $1,084.50