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 $53.45   11.467%   $59.5791   $59.58   $59.60   $59.60  
  Purchase #2 $104.77   11.480%   $116.7976   $116.80   $116.80   $116.80  
  Purchase #3 $95.37   4.407%   $99.573   $99.57   $99.55   $99.60  
  Purchase #4 $32.26   8.400%   $34.9698   $34.97   $34.95   $35.00  
  Purchase #5 $6.50   12.828%   $7.3338   $7.33   $7.35   $7.30  
  Purchase #6 $233.38   8.104%   $252.2931   $252.29   $252.30   $252.30  
  Purchase #7 $24.39   3.677%   $25.2868   $25.29   $25.30   $25.30  
  7 purchase totals = $550.12       $595.8332   $595.83   $595.85   $595.90