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 $73.77   7.517%   $79.3153   $79.32   $79.30   $79.30  
  Purchase #2 $115.42   4.283%   $120.3634   $120.36   $120.35   $120.40  
  Purchase #3 $53.53   10.871%   $59.3492   $59.35   $59.35   $59.30  
  Purchase #4 $222.46   3.716%   $230.7266   $230.73   $230.75   $230.70  
  Purchase #5 $169.77   9.698%   $186.2343   $186.23   $186.25   $186.20  
  Purchase #6 $147.75   12.526%   $166.2572   $166.26   $166.25   $166.30  
  Purchase #7 $198.94   7.385%   $213.6317   $213.63   $213.65   $213.60  
  7 purchase totals = $981.64       $1,055.8777   $1,055.88   $1,055.90   $1,055.80