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 $218.53   7.628%   $235.1995   $235.20   $235.20   $235.20  
  Purchase #2 $206.78   10.572%   $228.6408   $228.64   $228.65   $228.60  
  Purchase #3 $150.51   10.698%   $166.6116   $166.61   $166.60   $166.60  
  Purchase #4 $152.40   4.368%   $159.0568   $159.06   $159.05   $159.10  
  Purchase #5 $39.31   10.449%   $43.4175   $43.42   $43.40   $43.40  
  Purchase #6 $11.54   7.541%   $12.4102   $12.41   $12.40   $12.40  
  Purchase #7 $97.93   9.671%   $107.4008   $107.40   $107.40   $107.40  
  7 purchase totals = $877.00       $952.7372   $952.74   $952.70   $952.70