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 $57.69   11.318%   $64.2194   $64.22   $64.20   $64.20  
  Purchase #2 $215.57   12.155%   $241.7725   $241.77   $241.75   $241.80  
  Purchase #3 $119.99   5.784%   $126.9302   $126.93   $126.95   $126.90  
  Purchase #4 $104.49   10.459%   $115.4186   $115.42   $115.40   $115.40  
  Purchase #5 $142.62   4.727%   $149.3616   $149.36   $149.35   $149.40  
  Purchase #6 $168.84   7.176%   $180.956   $180.96   $180.95   $181.00  
  Purchase #7 $155.67   6.412%   $165.6516   $165.65   $165.65   $165.70  
  7 purchase totals = $964.87       $1,044.3099   $1,044.31   $1,044.25   $1,044.40