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 $58.27   8.693%   $63.3354   $63.34   $63.35   $63.30  
  Purchase #2 $142.59   9.224%   $155.7425   $155.74   $155.75   $155.70  
  Purchase #3 $244.67   10.250%   $269.7487   $269.75   $269.75   $269.70  
  Purchase #4 $48.93   4.757%   $51.2576   $51.26   $51.25   $51.30  
  Purchase #5 $173.46   6.510%   $184.7522   $184.75   $184.75   $184.80  
  Purchase #6 $177.47   10.216%   $195.6003   $195.60   $195.60   $195.60  
  Purchase #7 $126.25   3.495%   $130.6624   $130.66   $130.65   $130.70  
  7 purchase totals = $971.64       $1,051.0991   $1,051.10   $1,051.10   $1,051.10