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 $224.77   13.136%   $254.2958   $254.30   $254.30   $254.30  
  Purchase #2 $154.63   7.779%   $166.6587   $166.66   $166.65   $166.70  
  Purchase #3 $157.35   6.547%   $167.6517   $167.65   $167.65   $167.70  
  Purchase #4 $227.32   13.749%   $258.5742   $258.57   $258.55   $258.60  
  Purchase #5 $174.66   5.636%   $184.5038   $184.50   $184.50   $184.50  
  Purchase #6 $225.25   5.253%   $237.0824   $237.08   $237.10   $237.10  
  Purchase #7 $169.55   3.470%   $175.4334   $175.43   $175.45   $175.40  
  7 purchase totals = $1,333.53       $1,444.2000   $1,444.19   $1,444.20   $1,444.30