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 $141.66   9.542%   $155.1772   $155.18   $155.20   $155.20  
  Purchase #2 $33.38   6.304%   $35.4843   $35.48   $35.50   $35.50  
  Purchase #3 $25.26   3.748%   $26.2067   $26.21   $26.20   $26.20  
  Purchase #4 $134.26   12.427%   $150.9445   $150.94   $150.95   $150.90  
  Purchase #5 $93.29   3.292%   $96.3611   $96.36   $96.35   $96.40  
  Purchase #6 $123.68   4.508%   $129.2555   $129.26   $129.25   $129.30  
  Purchase #7 $250.29   4.820%   $262.354   $262.35   $262.35   $262.40  
  7 purchase totals = $801.82       $855.7833   $855.78   $855.80   $855.90