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 $111.38   10.676%   $123.2709   $123.27   $123.25   $123.30  
  Purchase #2 $60.61   3.209%   $62.555   $62.56   $62.55   $62.60  
  Purchase #3 $13.52   8.817%   $14.7121   $14.71   $14.70   $14.70  
  Purchase #4 $49.40   9.758%   $54.2205   $54.22   $54.20   $54.20  
  Purchase #5 $165.57   6.697%   $176.6582   $176.66   $176.65   $176.70  
  Purchase #6 $67.96   13.323%   $77.0143   $77.01   $77.00   $77.00  
  Purchase #7 $27.29   12.774%   $30.776   $30.78   $30.80   $30.80  
  7 purchase totals = $495.73       $539.2070   $539.21   $539.15   $539.30