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 $79.83   5.769%   $84.4354   $84.44   $84.45   $84.40  
  Purchase #2 $100.77   10.469%   $111.3196   $111.32   $111.30   $111.30  
  Purchase #3 $216.72   12.678%   $244.1958   $244.20   $244.20   $244.20  
  Purchase #4 $93.96   4.752%   $98.425   $98.43   $98.45   $98.40  
  Purchase #5 $159.52   9.170%   $174.148   $174.15   $174.15   $174.10  
  Purchase #6 $131.29   10.267%   $144.7695   $144.77   $144.75   $144.80  
  Purchase #7 $117.47   6.774%   $125.4274   $125.43   $125.45   $125.40  
  7 purchase totals = $899.56       $982.7207   $982.74   $982.75   $982.60