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 $70.50   8.759%   $76.6751   $76.68   $76.70   $76.70  
  Purchase #2 $239.75   10.743%   $265.5063   $265.51   $265.50   $265.50  
  Purchase #3 $243.40   10.552%   $269.0836   $269.08   $269.10   $269.10  
  Purchase #4 $85.38   8.505%   $92.6416   $92.64   $92.65   $92.60  
  Purchase #5 $56.25   7.438%   $60.4339   $60.43   $60.45   $60.40  
  Purchase #6 $207.29   10.869%   $229.8204   $229.82   $229.80   $229.80  
  Purchase #7 $164.39   3.723%   $170.5102   $170.51   $170.50   $170.50  
  7 purchase totals = $1,066.96       $1,164.6711   $1,164.67   $1,164.70   $1,164.60