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 $121.87   10.178%   $134.2739   $134.27   $134.25   $134.30  
  Purchase #2 $45.53   3.333%   $47.0475   $47.05   $47.05   $47.00  
  Purchase #3 $216.87   10.142%   $238.865   $238.87   $238.85   $238.90  
  Purchase #4 $229.68   10.603%   $254.033   $254.03   $254.05   $254.00  
  Purchase #5 $44.74   3.158%   $46.1529   $46.15   $46.15   $46.20  
  Purchase #6 $86.57   4.667%   $90.6102   $90.61   $90.60   $90.60  
  Purchase #7 $229.46   3.305%   $237.0437   $237.04   $237.05   $237.00  
  7 purchase totals = $974.72       $1,048.0262   $1,048.02   $1,048.00   $1,048.00