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 $37.86   13.725%   $43.0563   $43.06   $43.05   $43.10  
  Purchase #2 $32.95   3.471%   $34.0937   $34.09   $34.10   $34.10  
  Purchase #3 $166.52   5.520%   $175.7119   $175.71   $175.70   $175.70  
  Purchase #4 $63.90   7.216%   $68.511   $68.51   $68.50   $68.50  
  Purchase #5 $213.49   3.251%   $220.4306   $220.43   $220.45   $220.40  
  Purchase #6 $194.57   5.678%   $205.6177   $205.62   $205.60   $205.60  
  Purchase #7 $47.63   6.539%   $50.7445   $50.74   $50.75   $50.70  
  7 purchase totals = $756.92       $798.1657   $798.16   $798.15   $798.10