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 $59.97   13.869%   $68.2872   $68.29   $68.30   $68.30  
  Purchase #2 $111.55   5.727%   $117.9385   $117.94   $117.95   $117.90  
  Purchase #3 $188.80   3.493%   $195.3948   $195.39   $195.40   $195.40  
  Purchase #4 $102.26   12.234%   $114.7705   $114.77   $114.75   $114.80  
  Purchase #5 $213.91   12.704%   $241.0851   $241.09   $241.10   $241.10  
  Purchase #6 $125.31   3.846%   $130.1294   $130.13   $130.15   $130.10  
  Purchase #7 $213.28   7.348%   $228.9518   $228.95   $228.95   $229.00  
  7 purchase totals = $1,015.08       $1,096.5573   $1,096.56   $1,096.60   $1,096.60