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 $162.67   12.250%   $182.5971   $182.60   $182.60   $182.60  
  Purchase #2 $116.94   4.294%   $121.9614   $121.96   $121.95   $122.00  
  Purchase #3 $53.45   4.578%   $55.8969   $55.90   $55.90   $55.90  
  Purchase #4 $60.98   7.714%   $65.684   $65.68   $65.70   $65.70  
  Purchase #5 $131.45   9.701%   $144.202   $144.20   $144.20   $144.20  
  Purchase #6 $247.38   8.831%   $269.2261   $269.23   $269.25   $269.20  
  Purchase #7 $65.42   6.771%   $69.8496   $69.85   $69.85   $69.80  
  7 purchase totals = $838.29       $909.4171   $909.42   $909.45   $909.40