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 $87.66   8.681%   $95.2698   $95.27   $95.25   $95.30  
  Purchase #2 $64.32   3.656%   $66.6715   $66.67   $66.65   $66.70  
  Purchase #3 $49.57   13.202%   $56.1142   $56.11   $56.10   $56.10  
  Purchase #4 $200.77   5.790%   $212.3946   $212.39   $212.40   $212.40  
  Purchase #5 $92.62   7.508%   $99.5739   $99.57   $99.55   $99.60  
  Purchase #6 $128.63   4.276%   $134.1302   $134.13   $134.15   $134.10  
  Purchase #7 $35.97   7.562%   $38.6901   $38.69   $38.70   $38.70  
  7 purchase totals = $659.54       $702.8443   $702.83   $702.80   $702.90