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 $71.99   4.231%   $75.0359   $75.04   $75.05   $75.00  
  Purchase #2 $119.77   8.740%   $130.2379   $130.24   $130.25   $130.20  
  Purchase #3 $223.31   5.434%   $235.4447   $235.44   $235.45   $235.40  
  Purchase #4 $175.36   7.526%   $188.5576   $188.56   $188.55   $188.60  
  Purchase #5 $202.65   8.716%   $220.313   $220.31   $220.30   $220.30  
  Purchase #6 $145.53   4.787%   $152.4965   $152.50   $152.50   $152.50  
  Purchase #7 $50.73   13.860%   $57.7612   $57.76   $57.75   $57.80  
  7 purchase totals = $989.34       $1,059.8468   $1,059.85   $1,059.85   $1,059.80