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 $83.64   12.313%   $93.9386   $93.94   $93.95   $93.90  
  Purchase #2 $33.98   3.706%   $35.2393   $35.24   $35.25   $35.20  
  Purchase #3 $148.43   7.636%   $159.7641   $159.76   $159.75   $159.80  
  Purchase #4 $250.37   5.414%   $263.925   $263.93   $263.95   $263.90  
  Purchase #5 $226.75   10.357%   $250.2345   $250.23   $250.25   $250.20  
  Purchase #6 $228.83   10.329%   $252.4659   $252.47   $252.45   $252.50  
  Purchase #7 $88.45   7.452%   $95.0413   $95.04   $95.05   $95.00  
  7 purchase totals = $1,060.45       $1,150.6087   $1,150.61   $1,150.65   $1,150.50