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 $57.38   13.286%   $65.0035   $65.00   $65.00   $65.00  
  Purchase #2 $152.30   12.279%   $171.0009   $171.00   $171.00   $171.00  
  Purchase #3 $77.53   12.702%   $87.3779   $87.38   $87.40   $87.40  
  Purchase #4 $76.58   6.828%   $81.8089   $81.81   $81.80   $81.80  
  Purchase #5 $165.39   11.646%   $184.6513   $184.65   $184.65   $184.70  
  Purchase #6 $73.95   7.275%   $79.3299   $79.33   $79.35   $79.30  
  Purchase #7 $50.98   5.474%   $53.7706   $53.77   $53.75   $53.80  
  7 purchase totals = $654.11       $722.9430   $722.94   $722.95   $723.00