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 $55.33   4.213%   $57.6611   $57.66   $57.65   $57.70  
  Purchase #2 $218.33   12.230%   $245.0318   $245.03   $245.05   $245.00  
  Purchase #3 $199.88   12.115%   $224.0955   $224.10   $224.10   $224.10  
  Purchase #4 $56.52   7.574%   $60.8008   $60.80   $60.80   $60.80  
  Purchase #5 $184.47   12.270%   $207.1045   $207.10   $207.10   $207.10  
  Purchase #6 $210.70   13.819%   $239.8166   $239.82   $239.80   $239.80  
  Purchase #7 $62.76   3.640%   $65.0445   $65.04   $65.05   $65.00  
  7 purchase totals = $987.99       $1,099.5548   $1,099.55   $1,099.55   $1,099.50