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 $54.40   11.259%   $60.5249   $60.52   $60.50   $60.50  
  Purchase #2 $72.97   4.231%   $76.0574   $76.06   $76.05   $76.10  
  Purchase #3 $213.55   8.244%   $231.1551   $231.16   $231.15   $231.20  
  Purchase #4 $201.76   4.435%   $210.7081   $210.71   $210.70   $210.70  
  Purchase #5 $225.68   8.671%   $245.2487   $245.25   $245.25   $245.20  
  Purchase #6 $70.88   12.566%   $79.7868   $79.79   $79.80   $79.80  
  Purchase #7 $142.36   10.270%   $156.9804   $156.98   $157.00   $157.00  
  7 purchase totals = $981.60       $1,060.4614   $1,060.47   $1,060.45   $1,060.50