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 $191.67   8.277%   $207.5345   $207.53   $207.55   $207.50  
  Purchase #2 $48.25   9.444%   $52.8067   $52.81   $52.80   $52.80  
  Purchase #3 $60.58   11.227%   $67.3813   $67.38   $67.40   $67.40  
  Purchase #4 $184.79   7.459%   $198.5735   $198.57   $198.55   $198.60  
  Purchase #5 $246.68   7.657%   $265.5683   $265.57   $265.55   $265.60  
  Purchase #6 $55.80   4.254%   $58.1737   $58.17   $58.15   $58.20  
  Purchase #7 $108.51   4.611%   $113.5134   $113.51   $113.50   $113.50  
  7 purchase totals = $896.28       $963.5514   $963.54   $963.50   $963.60