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 $23.65   11.404%   $26.347   $26.35   $26.35   $26.30  
  Purchase #2 $120.35   5.263%   $126.684   $126.68   $126.70   $126.70  
  Purchase #3 $167.43   9.495%   $183.3275   $183.33   $183.35   $183.30  
  Purchase #4 $100.95   10.191%   $111.2378   $111.24   $111.25   $111.20  
  Purchase #5 $88.95   8.413%   $96.4334   $96.43   $96.45   $96.40  
  Purchase #6 $243.69   5.289%   $256.5788   $256.58   $256.60   $256.60  
  Purchase #7 $130.41   4.192%   $135.8768   $135.88   $135.90   $135.90  
  7 purchase totals = $875.43       $936.4853   $936.49   $936.60   $936.40