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 $51.47   7.239%   $55.1959   $55.20   $55.20   $55.20  
  Purchase #2 $175.83   4.504%   $183.7494   $183.75   $183.75   $183.70  
  Purchase #3 $243.34   3.482%   $251.8131   $251.81   $251.80   $251.80  
  Purchase #4 $201.53   13.382%   $228.4987   $228.50   $228.50   $228.50  
  Purchase #5 $60.32   11.270%   $67.1181   $67.12   $67.10   $67.10  
  Purchase #6 $117.85   5.830%   $124.7207   $124.72   $124.70   $124.70  
  Purchase #7 $101.52   11.717%   $113.4151   $113.42   $113.40   $113.40  
  7 purchase totals = $951.86       $1,024.5110   $1,024.52   $1,024.45   $1,024.40