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 $238.91   11.208%   $265.687   $265.69   $265.70   $265.70  
  Purchase #2 $153.74   4.287%   $160.3308   $160.33   $160.35   $160.30  
  Purchase #3 $167.66   4.153%   $174.6229   $174.62   $174.60   $174.60  
  Purchase #4 $21.79   3.639%   $22.5829   $22.58   $22.60   $22.60  
  Purchase #5 $101.30   5.175%   $106.5423   $106.54   $106.55   $106.50  
  Purchase #6 $222.91   9.814%   $244.7864   $244.79   $244.80   $244.80  
  Purchase #7 $38.27   3.166%   $39.4816   $39.48   $39.50   $39.50  
  7 purchase totals = $944.58       $1,014.0339   $1,014.03   $1,014.10   $1,014.00