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 $241.70   9.597%   $264.8959   $264.90   $264.90   $264.90  
  Purchase #2 $25.44   4.235%   $26.5174   $26.52   $26.50   $26.50  
  Purchase #3 $57.75   13.158%   $65.3487   $65.35   $65.35   $65.30  
  Purchase #4 $131.86   10.120%   $145.2042   $145.20   $145.20   $145.20  
  Purchase #5 $117.75   4.165%   $122.6543   $122.65   $122.65   $122.70  
  Purchase #6 $32.28   5.323%   $33.9983   $34.00   $34.00   $34.00  
  Purchase #7 $160.93   8.235%   $174.1826   $174.18   $174.20   $174.20  
  7 purchase totals = $767.71       $832.8014   $832.80   $832.80   $832.80