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 $219.98   6.200%   $233.6188   $233.62   $233.60   $233.60  
  Purchase #2 $228.74   5.818%   $242.0481   $242.05   $242.05   $242.00  
  Purchase #3 $66.93   11.557%   $74.6651   $74.67   $74.65   $74.70  
  Purchase #4 $246.74   13.372%   $279.7341   $279.73   $279.75   $279.70  
  Purchase #5 $50.96   8.228%   $55.153   $55.15   $55.15   $55.20  
  Purchase #6 $200.36   6.784%   $213.9524   $213.95   $213.95   $214.00  
  Purchase #7 $224.96   12.115%   $252.2139   $252.21   $252.20   $252.20  
  7 purchase totals = $1,238.67       $1,351.3854   $1,351.38   $1,351.35   $1,351.40