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 $216.57   12.162%   $242.9092   $242.91   $242.90   $242.90  
  Purchase #2 $237.68   11.774%   $265.6644   $265.66   $265.65   $265.70  
  Purchase #3 $171.39   8.132%   $185.3274   $185.33   $185.35   $185.30  
  Purchase #4 $160.73   12.669%   $181.0929   $181.09   $181.10   $181.10  
  Purchase #5 $7.52   5.213%   $7.912   $7.91   $7.90   $7.90  
  Purchase #6 $66.91   11.721%   $74.7525   $74.75   $74.75   $74.80  
  Purchase #7 $8.50   6.578%   $9.0591   $9.06   $9.05   $9.10  
  7 purchase totals = $869.30       $966.7175   $966.71   $966.70   $966.80