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 $44.33   10.132%   $48.8215   $48.82   $48.80   $48.80  
  Purchase #2 $114.37   4.728%   $119.7774   $119.78   $119.80   $119.80  
  Purchase #3 $109.55   13.227%   $124.0402   $124.04   $124.05   $124.00  
  Purchase #4 $66.54   5.613%   $70.2749   $70.27   $70.25   $70.30  
  Purchase #5 $200.32   3.748%   $207.828   $207.83   $207.85   $207.80  
  Purchase #6 $221.44   3.220%   $228.5704   $228.57   $228.55   $228.60  
  Purchase #7 $209.75   5.136%   $220.5228   $220.52   $220.50   $220.50  
  7 purchase totals = $966.30       $1,019.8352   $1,019.83   $1,019.80   $1,019.80