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 $50.68   5.852%   $53.6458   $53.65   $53.65   $53.60  
  Purchase #2 $72.89   9.357%   $79.7103   $79.71   $79.70   $79.70  
  Purchase #3 $128.69   13.347%   $145.8663   $145.87   $145.85   $145.90  
  Purchase #4 $168.95   9.123%   $184.3633   $184.36   $184.35   $184.40  
  Purchase #5 $73.41   5.654%   $77.5606   $77.56   $77.55   $77.60  
  Purchase #6 $243.63   11.242%   $271.0189   $271.02   $271.00   $271.00  
  Purchase #7 $231.29   3.546%   $239.4915   $239.49   $239.50   $239.50  
  7 purchase totals = $969.54       $1,051.6567   $1,051.66   $1,051.60   $1,051.70