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 $79.78   3.534%   $82.5994   $82.60   $82.60   $82.60  
  Purchase #2 $132.81   10.705%   $147.0273   $147.03   $147.05   $147.00  
  Purchase #3 $54.55   8.248%   $59.0493   $59.05   $59.05   $59.00  
  Purchase #4 $146.91   3.575%   $152.162   $152.16   $152.15   $152.20  
  Purchase #5 $6.53   4.315%   $6.8118   $6.81   $6.80   $6.80  
  Purchase #6 $219.91   11.253%   $244.6565   $244.66   $244.65   $244.70  
  Purchase #7 $166.65   4.422%   $174.0193   $174.02   $174.00   $174.00  
  7 purchase totals = $807.14       $866.3256   $866.33   $866.30   $866.30