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 $144.82   4.377%   $151.1588   $151.16   $151.15   $151.20  
  Purchase #2 $10.98   8.646%   $11.9293   $11.93   $11.95   $11.90  
  Purchase #3 $29.54   12.311%   $33.1767   $33.18   $33.20   $33.20  
  Purchase #4 $26.91   7.448%   $28.9143   $28.91   $28.90   $28.90  
  Purchase #5 $188.79   10.514%   $208.6394   $208.64   $208.65   $208.60  
  Purchase #6 $40.56   6.646%   $43.2556   $43.26   $43.25   $43.30  
  Purchase #7 $209.49   7.452%   $225.1012   $225.10   $225.10   $225.10  
  7 purchase totals = $651.09       $702.1753   $702.18   $702.20   $702.20