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 $15.26   10.819%   $16.911   $16.91   $16.90   $16.90  
  Purchase #2 $228.53   8.187%   $247.2398   $247.24   $247.25   $247.20  
  Purchase #3 $129.92   12.286%   $145.882   $145.88   $145.90   $145.90  
  Purchase #4 $218.93   7.196%   $234.6842   $234.68   $234.70   $234.70  
  Purchase #5 $101.51   9.408%   $111.0601   $111.06   $111.05   $111.10  
  Purchase #6 $189.49   9.213%   $206.9477   $206.95   $206.95   $206.90  
  Purchase #7 $61.52   3.672%   $63.779   $63.78   $63.80   $63.80  
  7 purchase totals = $945.16       $1,026.5038   $1,026.50   $1,026.55   $1,026.50