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 $65.26   12.660%   $73.5219   $73.52   $73.50   $73.50  
  Purchase #2 $76.60   6.771%   $81.7866   $81.79   $81.80   $81.80  
  Purchase #3 $169.60   5.290%   $178.5718   $178.57   $178.55   $178.60  
  Purchase #4 $5.30   5.627%   $5.5982   $5.60   $5.60   $5.60  
  Purchase #5 $15.42   11.801%   $17.2397   $17.24   $17.25   $17.20  
  Purchase #6 $147.96   13.558%   $168.0204   $168.02   $168.00   $168.00  
  Purchase #7 $124.92   11.288%   $139.021   $139.02   $139.00   $139.00  
  7 purchase totals = $605.06       $663.7596   $663.76   $663.70   $663.70