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 $93.56   3.110%   $96.4697   $96.47   $96.45   $96.50  
  Purchase #2 $120.92   8.854%   $131.6263   $131.63   $131.65   $131.60  
  Purchase #3 $168.32   5.787%   $178.0607   $178.06   $178.05   $178.10  
  Purchase #4 $106.51   13.119%   $120.483   $120.48   $120.50   $120.50  
  Purchase #5 $65.85   4.609%   $68.885   $68.89   $68.90   $68.90  
  Purchase #6 $163.73   5.109%   $172.095   $172.10   $172.10   $172.10  
  Purchase #7 $173.26   9.474%   $189.6747   $189.67   $189.65   $189.70  
  7 purchase totals = $892.15       $957.2944   $957.30   $957.30   $957.40