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 $58.41   8.810%   $63.5559   $63.56   $63.55   $63.60  
  Purchase #2 $53.75   9.621%   $58.9213   $58.92   $58.90   $58.90  
  Purchase #3 $56.48   13.348%   $64.019   $64.02   $64.00   $64.00  
  Purchase #4 $55.65   3.848%   $57.7914   $57.79   $57.80   $57.80  
  Purchase #5 $188.70   8.816%   $205.3358   $205.34   $205.35   $205.30  
  Purchase #6 $222.93   5.549%   $235.3004   $235.30   $235.30   $235.30  
  Purchase #7 $47.55   3.593%   $49.2585   $49.26   $49.25   $49.30  
  7 purchase totals = $683.47       $734.1823   $734.19   $734.15   $734.20