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 $50.99   13.803%   $58.0281   $58.03   $58.05   $58.00  
  Purchase #2 $113.66   9.667%   $124.6475   $124.65   $124.65   $124.60  
  Purchase #3 $82.59   6.193%   $87.7048   $87.70   $87.70   $87.70  
  Purchase #4 $49.26   6.219%   $52.3235   $52.32   $52.30   $52.30  
  Purchase #5 $249.92   7.685%   $269.1264   $269.13   $269.15   $269.10  
  Purchase #6 $53.80   9.842%   $59.095   $59.10   $59.10   $59.10  
  Purchase #7 $240.69   11.379%   $268.0781   $268.08   $268.10   $268.10  
  7 purchase totals = $840.91       $919.0034   $919.01   $919.05   $918.90