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 $36.96   11.162%   $41.0855   $41.09   $41.10   $41.10  
  Purchase #2 $196.70   3.521%   $203.6258   $203.63   $203.65   $203.60  
  Purchase #3 $134.37   9.585%   $147.2494   $147.25   $147.25   $147.20  
  Purchase #4 $235.77   4.732%   $246.9266   $246.93   $246.95   $246.90  
  Purchase #5 $71.38   4.354%   $74.4879   $74.49   $74.50   $74.50  
  Purchase #6 $54.60   6.386%   $58.0868   $58.09   $58.10   $58.10  
  Purchase #7 $29.51   3.375%   $30.506   $30.51   $30.50   $30.50  
  7 purchase totals = $759.29       $801.9680   $801.99   $802.05   $801.90