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 $58.81   13.820%   $66.9375   $66.94   $66.95   $66.90  
  Purchase #2 $157.37   12.812%   $177.5322   $177.53   $177.55   $177.50  
  Purchase #3 $246.56   7.567%   $265.2172   $265.22   $265.20   $265.20  
  Purchase #4 $60.57   12.259%   $67.9953   $68.00   $68.00   $68.00  
  Purchase #5 $10.91   4.846%   $11.4387   $11.44   $11.45   $11.40  
  Purchase #6 $222.74   3.472%   $230.4735   $230.47   $230.45   $230.50  
  Purchase #7 $16.79   6.619%   $17.9013   $17.90   $17.90   $17.90  
  7 purchase totals = $773.75       $837.4957   $837.50   $837.50   $837.40