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 $119.93   13.566%   $136.1997   $136.20   $136.20   $136.20  
  Purchase #2 $187.46   13.605%   $212.9639   $212.96   $212.95   $213.00  
  Purchase #3 $174.36   4.810%   $182.7467   $182.75   $182.75   $182.70  
  Purchase #4 $17.72   10.854%   $19.6433   $19.64   $19.65   $19.60  
  Purchase #5 $202.50   3.617%   $209.8244   $209.82   $209.80   $209.80  
  Purchase #6 $198.48   7.160%   $212.6912   $212.69   $212.70   $212.70  
  Purchase #7 $41.39   3.791%   $42.9591   $42.96   $42.95   $43.00  
  7 purchase totals = $941.84       $1,017.0283   $1,017.02   $1,017.00   $1,017.00