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 $68.25   13.453%   $77.4317   $77.43   $77.45   $77.40  
  Purchase #2 $151.71   9.779%   $166.5457   $166.55   $166.55   $166.50  
  Purchase #3 $63.80   13.744%   $72.5687   $72.57   $72.55   $72.60  
  Purchase #4 $191.96   4.834%   $201.2393   $201.24   $201.25   $201.20  
  Purchase #5 $143.74   5.526%   $151.6831   $151.68   $151.70   $151.70  
  Purchase #6 $43.43   6.149%   $46.1005   $46.10   $46.10   $46.10  
  Purchase #7 $138.66   6.139%   $147.1723   $147.17   $147.15   $147.20  
  7 purchase totals = $801.55       $862.7413   $862.74   $862.75   $862.70