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 $202.68   10.268%   $223.4912   $223.49   $223.50   $223.50  
  Purchase #2 $24.51   6.769%   $26.1691   $26.17   $26.15   $26.20  
  Purchase #3 $67.49   6.644%   $71.974   $71.97   $71.95   $72.00  
  Purchase #4 $80.74   3.799%   $83.8073   $83.81   $83.80   $83.80  
  Purchase #5 $87.47   6.329%   $93.006   $93.01   $93.00   $93.00  
  Purchase #6 $223.75   4.595%   $234.0313   $234.03   $234.05   $234.00  
  Purchase #7 $184.35   3.547%   $190.8889   $190.89   $190.90   $190.90  
  7 purchase totals = $870.99       $923.3678   $923.37   $923.35   $923.40