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 $70.67   4.677%   $73.9752   $73.98   $74.00   $74.00  
  Purchase #2 $220.86   13.493%   $250.6606   $250.66   $250.65   $250.70  
  Purchase #3 $184.87   4.192%   $192.6198   $192.62   $192.60   $192.60  
  Purchase #4 $113.83   8.657%   $123.6843   $123.68   $123.70   $123.70  
  Purchase #5 $120.95   11.122%   $134.4021   $134.40   $134.40   $134.40  
  Purchase #6 $189.51   7.691%   $204.0852   $204.09   $204.10   $204.10  
  Purchase #7 $110.30   3.323%   $113.9653   $113.97   $113.95   $114.00  
  7 purchase totals = $1,010.99       $1,093.3925   $1,093.40   $1,093.40   $1,093.50