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 $57.66   7.248%   $61.8392   $61.84   $61.85   $61.80  
  Purchase #2 $55.46   11.366%   $61.7636   $61.76   $61.75   $61.80  
  Purchase #3 $239.52   3.455%   $247.7954   $247.80   $247.80   $247.80  
  Purchase #4 $118.75   4.488%   $124.0795   $124.08   $124.10   $124.10  
  Purchase #5 $160.28   9.370%   $175.2982   $175.30   $175.30   $175.30  
  Purchase #6 $217.57   12.791%   $245.3994   $245.40   $245.40   $245.40  
  Purchase #7 $90.84   5.466%   $95.8053   $95.81   $95.80   $95.80  
  7 purchase totals = $940.08       $1,011.9806   $1,011.99   $1,012.00   $1,012.00