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 $49.34   9.350%   $53.9533   $53.95   $53.95   $54.00  
  Purchase #2 $5.82   4.787%   $6.0986   $6.10   $6.10   $6.10  
  Purchase #3 $180.77   8.845%   $196.7591   $196.76   $196.75   $196.80  
  Purchase #4 $240.89   10.809%   $266.9278   $266.93   $266.95   $266.90  
  Purchase #5 $58.61   3.479%   $60.649   $60.65   $60.65   $60.60  
  Purchase #6 $197.99   10.703%   $219.1809   $219.18   $219.20   $219.20  
  Purchase #7 $60.79   7.679%   $65.4581   $65.46   $65.45   $65.50  
  7 purchase totals = $794.21       $869.0268   $869.03   $869.05   $869.10