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 $41.58   7.372%   $44.6453   $44.65   $44.65   $44.60  
  Purchase #2 $215.92   6.268%   $229.4539   $229.45   $229.45   $229.50  
  Purchase #3 $36.54   5.581%   $38.5793   $38.58   $38.60   $38.60  
  Purchase #4 $6.69   5.468%   $7.0558   $7.06   $7.05   $7.10  
  Purchase #5 $198.84   3.672%   $206.1414   $206.14   $206.15   $206.10  
  Purchase #6 $246.46   12.261%   $276.6785   $276.68   $276.70   $276.70  
  Purchase #7 $98.70   10.129%   $108.6973   $108.70   $108.70   $108.70  
  7 purchase totals = $844.73       $911.2515   $911.26   $911.30   $911.30