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 $22.31   8.711%   $24.2534   $24.25   $24.25   $24.30  
  Purchase #2 $208.98   13.572%   $237.3428   $237.34   $237.35   $237.30  
  Purchase #3 $157.35   12.799%   $177.4892   $177.49   $177.50   $177.50  
  Purchase #4 $240.61   6.372%   $255.9417   $255.94   $255.95   $255.90  
  Purchase #5 $246.68   8.250%   $267.0311   $267.03   $267.05   $267.00  
  Purchase #6 $23.88   11.623%   $26.6556   $26.66   $26.65   $26.70  
  Purchase #7 $26.25   9.414%   $28.7212   $28.72   $28.70   $28.70  
  7 purchase totals = $926.06       $1,017.4350   $1,017.43   $1,017.45   $1,017.40