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 $161.46   13.739%   $183.643   $183.64   $183.65   $183.60  
  Purchase #2 $226.37   8.579%   $245.7903   $245.79   $245.80   $245.80  
  Purchase #3 $17.71   5.220%   $18.6345   $18.63   $18.65   $18.60  
  Purchase #4 $41.82   8.336%   $45.3061   $45.31   $45.30   $45.30  
  Purchase #5 $109.66   13.126%   $124.054   $124.05   $124.05   $124.10  
  Purchase #6 $57.92   10.656%   $64.092   $64.09   $64.10   $64.10  
  Purchase #7 $208.98   8.203%   $226.1226   $226.12   $226.10   $226.10  
  7 purchase totals = $823.92       $907.6425   $907.63   $907.65   $907.60