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 $87.85   7.252%   $94.2209   $94.22   $94.20   $94.20  
  Purchase #2 $231.35   9.187%   $252.6041   $252.60   $252.60   $252.60  
  Purchase #3 $53.51   10.239%   $58.9889   $58.99   $59.00   $59.00  
  Purchase #4 $135.72   4.405%   $141.6985   $141.70   $141.70   $141.70  
  Purchase #5 $95.93   11.397%   $106.8631   $106.86   $106.85   $106.90  
  Purchase #6 $73.91   13.403%   $83.8162   $83.82   $83.80   $83.80  
  Purchase #7 $19.75   9.577%   $21.6415   $21.64   $21.65   $21.60  
  7 purchase totals = $698.02       $759.8332   $759.83   $759.80   $759.80