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 $134.34   13.298%   $152.2045   $152.20   $152.20   $152.20  
  Purchase #2 $200.66   12.127%   $224.994   $224.99   $225.00   $225.00  
  Purchase #3 $60.31   13.581%   $68.5007   $68.50   $68.50   $68.50  
  Purchase #4 $208.39   9.779%   $228.7685   $228.77   $228.75   $228.80  
  Purchase #5 $124.61   4.564%   $130.2972   $130.30   $130.30   $130.30  
  Purchase #6 $85.97   9.151%   $93.8371   $93.84   $93.85   $93.80  
  Purchase #7 $135.50   9.282%   $148.0771   $148.08   $148.10   $148.10  
  7 purchase totals = $949.78       $1,046.6791   $1,046.68   $1,046.70   $1,046.70