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 $93.41   3.544%   $96.7205   $96.72   $96.70   $96.70  
  Purchase #2 $154.49   8.399%   $167.4656   $167.47   $167.45   $167.50  
  Purchase #3 $225.74   10.205%   $248.7768   $248.78   $248.80   $248.80  
  Purchase #4 $179.32   6.525%   $191.0206   $191.02   $191.00   $191.00  
  Purchase #5 $149.62   13.150%   $169.295   $169.30   $169.30   $169.30  
  Purchase #6 $229.47   10.747%   $254.1311   $254.13   $254.15   $254.10  
  Purchase #7 $243.25   9.279%   $265.8212   $265.82   $265.80   $265.80  
  7 purchase totals = $1,275.30       $1,393.2308   $1,393.24   $1,393.20   $1,393.20