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 $61.75   13.243%   $69.9276   $69.93   $69.95   $69.90  
  Purchase #2 $245.84   7.789%   $264.9885   $264.99   $265.00   $265.00  
  Purchase #3 $104.93   8.237%   $113.5731   $113.57   $113.55   $113.60  
  Purchase #4 $204.46   7.423%   $219.6371   $219.64   $219.65   $219.60  
  Purchase #5 $187.77   10.679%   $207.822   $207.82   $207.80   $207.80  
  Purchase #6 $32.57   8.642%   $35.3847   $35.38   $35.40   $35.40  
  Purchase #7 $8.60   9.618%   $9.4271   $9.43   $9.45   $9.40  
  7 purchase totals = $845.92       $920.7601   $920.76   $920.80   $920.70