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 $36.95   12.217%   $41.4642   $41.46   $41.45   $41.50  
  Purchase #2 $172.59   6.842%   $184.3986   $184.40   $184.40   $184.40  
  Purchase #3 $221.92   3.166%   $228.946   $228.95   $228.95   $228.90  
  Purchase #4 $53.64   5.803%   $56.7527   $56.75   $56.75   $56.80  
  Purchase #5 $195.66   7.858%   $211.035   $211.04   $211.05   $211.00  
  Purchase #6 $205.28   11.409%   $228.7004   $228.70   $228.70   $228.70  
  Purchase #7 $14.33   9.695%   $15.7193   $15.72   $15.70   $15.70  
  7 purchase totals = $900.37       $967.0162   $967.02   $967.00   $967.00