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 $60.77   6.857%   $64.937   $64.94   $64.95   $64.90  
  Purchase #2 $67.28   3.362%   $69.542   $69.54   $69.55   $69.50  
  Purchase #3 $186.25   6.813%   $198.9392   $198.94   $198.95   $198.90  
  Purchase #4 $41.45   6.785%   $44.2624   $44.26   $44.25   $44.30  
  Purchase #5 $197.28   11.366%   $219.7028   $219.70   $219.70   $219.70  
  Purchase #6 $243.57   9.449%   $266.5849   $266.58   $266.60   $266.60  
  Purchase #7 $83.25   4.692%   $87.1561   $87.16   $87.15   $87.20  
  7 purchase totals = $879.85       $951.1244   $951.12   $951.15   $951.10