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 $158.64   6.341%   $168.6994   $168.70   $168.70   $168.70  
  Purchase #2 $147.48   5.666%   $155.8362   $155.84   $155.85   $155.80  
  Purchase #3 $124.68   7.841%   $134.4562   $134.46   $134.45   $134.50  
  Purchase #4 $165.74   12.142%   $185.8642   $185.86   $185.85   $185.90  
  Purchase #5 $48.25   8.349%   $52.2784   $52.28   $52.30   $52.30  
  Purchase #6 $77.64   6.238%   $82.4832   $82.48   $82.50   $82.50  
  Purchase #7 $154.49   11.753%   $172.6472   $172.65   $172.65   $172.60  
  7 purchase totals = $876.92       $952.2648   $952.27   $952.30   $952.30