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 $186.74   3.291%   $192.8856   $192.89   $192.90   $192.90  
  Purchase #2 $150.94   3.782%   $156.6486   $156.65   $156.65   $156.60  
  Purchase #3 $247.84   4.748%   $259.6074   $259.61   $259.60   $259.60  
  Purchase #4 $160.45   6.755%   $171.2884   $171.29   $171.30   $171.30  
  Purchase #5 $79.86   7.146%   $85.5668   $85.57   $85.55   $85.60  
  Purchase #6 $137.30   3.176%   $141.6606   $141.66   $141.65   $141.70  
  Purchase #7 $216.98   3.724%   $225.0603   $225.06   $225.05   $225.10  
  7 purchase totals = $1,180.11       $1,232.7177   $1,232.73   $1,232.70   $1,232.80